Yahoo Gemini API - Allows advertisers to manage complex Gemini accounts and campaigns more efficiently.
Analytics
Amazon Mobile Analytics - Service for collecting, visualizing, and understanding app usage data at scale.
Clicky - Allows you to extract your web site's traffic data into several formats, making it easy to integrate, analyze, or store your data within your own application.
Countly - Self-hosted or private cloud mobile, web and desktop analytics.
Fabric - A platform that helps your mobile team build better apps, understand your users, and grow your business.
Flurry - Yahoo’s Flurry provides you with a number of APIs enabling you to export your data.
Google Analytics - Google Analytics provides APIs to collect, configure, and report on user-interactions with your online content.
envoice - Invoicing for online businesses. Simplify your invoicing process and get paid online with a debit or credit card via your payment gateway.
koomalooma - A Loyalty BPaaS (Business Process as a Service) for mobile and web companies. Merchants issue points for actions their customers/users make, for example a purchase or a referral. koomalooma takes care of all the rest, from signing up users, keeping track of points and delivering rewards in over 80 countries.đź’¸
Marketcloud - eCommerce APIs for developers. It covers inventory and database, carts and checkout, payments, user authentication, and more. You just bring the frontend.
Moltin - Unified APIs for inventory, carts, the checkout process, payments and more, so you can focus on creating seamless customer experiences at any scale.
Stripe - Allows both private individuals and businesses to accept payments over the Internet.
Braintree - Specializes in mobile and web payment systems for ecommerce companies.
Communication
Africa's Talking - Access African telco services through a HTTP API.đź’¸
Exotel - Exotel is a cloud telephony service provider for small and medium enterprises in India. Free 15-day trial.đź’¸
MailGun - Transactional Email API Service For Developers. Free first 10000 emails per month.đź’¸
Nexmo - Make and receive phone calls, send and receive SMS worldwide. Libraries in Node, Ruby, Java, PHP, .NET & Python.đź’¸
The SMS Works - The SMS Works provides a low-cost, reliable SMS API for developers. Pay only for delivered texts, all failed messages are refunded.đź’¸
Content
qKast Channel Content - Access live content collections sourced from any page around the web.
DictService - This Web Service allows you to access dictionary definitions from the dict.org service.
Glosbe API - Dictionary API and Translation Memory API description.
Merriam-Webster Dictionary API - Gives developers access to a big ass resource of dictionary and thesaurus content as well as specialized medical, Spanish, ESL, and student-friendly vocabulary.
Oxford Dictionary API - Access to Oxford Dictionary services with several different subscription options including a free tier. đź’¸
Pearson Dictionaries API - (BETA) Gives access to a very large database of words and phrases with thorough explanations - free usage for up to 4 million calls/month.
Swapi - Star Wars API with data you didn't even know existed, or that you needed to know.
Events
Picatic - Sell tickets directly from your app or website.
Face Recognition
Kairos - Face recognition, emotion analysis and measuring engagement of people in images or videos for any mobile or web application. 30 Day Trial đź’¸
Skybiometry - Face detection, emotional analysis, face grouping, recognition service and tagging the photo.
File Storage and Manipulation
Amazon S3 - API that provides access to stored files and can be added easily to any service - and it's free for twelve months.
Cloudinary - API for image and video storage and manipulation - free for up to 75,000 images and 7,500 manipulations per month, good documentation, it can also manipulate GIFs and PDFs.
Dropbox - API for accessing stored files and pictures which is easy to use and free for small amounts of data.
Filestack - API for image and file manipulation, 250 uploads and 500 uploads per month for free, free CDN, HTML widget.
Microsoft Graph - API for accessing stored files and photos for personal and enterprise users with high resolution thumbnails and Microsoft Office APIs.
Verizon Cloud - API for accessing stored pictures and other files stored by users of Verizon Cloud app.
Yogurl - API and CLI for serving files and code over HTTP instantly
RF - variety of data via REST XML and SOAP APIs. Some data is available only via the RESTful one, some is only via the SOAP one.
Switzerland - rich variety of datan in XLS and CSV formats.
Ukraine - exchange rates and bond placements in JSON and XML formats.
Fitness
FitBit - Web API for accessing data from Fitbit activity trackers, Aria scale, and manually entered logs.
HealthGraph - RunKeeper's web-based HealthGraph API presents Health Graph data, and provides information about a user and friends.
Lumo - The Lumo API provides access to detailed user activity with 5 minute resolution as well as access to user profile information, such as height, weight, gender, etc.
Strava - API for accessing and managing data about athletes, activities and segments.
Withings - Access to data from Withings activity trackers and body measures.
USDA API - United States Department of Agriculture Open Source API for gathering nutritional data, and food reports.
Google Monitoring API - API for accessing Google Cloud and API monitoring data. v2beta2
Identity Verification
BlockScore - A real-time API for verifying an identity by name, address, date of birth, and social security number.
Cognito - A powerful API for verifying and retrieving identity information. Can take a customer's cellphone number and return name, address history, full SSN, and date of birth.
Whitepages Pro - Global Identity Verification API. Get a clearer picture of your customer. Instantly know if a name, address, phone number, email, and IP all belong to the same person. Every country in the world supported. đź’¸
Image Moderation
Clarifai - AI API that analyzes images and videos and returns probability scores on the likelihood that the image contains pornography.
NullNude.com - The adult content detection API. Free for 600 images per month. đź’¸
WebPurify - Provides live image moderation by humans. Free for first 100 images. 2¢ per image after. 💸
IoT
Lelylan - Open Source Internet of Things Cloud Platform. Microservices Architecture. For Developers.
Particle - API to manage Particle devices (including their own Arduino-compatible ones and the Raspberry Pi) and control them. Free for up to 25 devices and 250k events/month.
PubNub - API to make realtime applications with variety of hardware devices including Arduino, RPi, Kinoma, Atmel, Samsung Smart TV WebOS, and more.
Philips Hue - Registration (free) and local Hue Bridge (not free) required - Control Hue brand lights made by Philips. API calls are made to the Hue Bridge residing on local network. Includes a web based UI.
SmartThings - API for Samsung SmartThings Smart Home Hub products (ZigBee, Z-Wave, IP).
Temboo SDK - This platform acts as a layer on top of third-party APIs, using code snippets to trigger complex processes that run through their cloud platform.
ThingSpeak - “Internet of Things” application and API to store and retrieve data from things using HTTP over the Internet or via a Local Area Network.
Xively - Uses free and open libraries to let you connect different types of hardware, using a variety of languages to their cloud service.
Zetta - An open source platform built on Node.js for creating IoT servers that run across geo-distributed computers and the cloud.
PayPal - Enables your customers to sign in to your web site quickly and securely using their PayPal login credentials.
Salesforce - Salesforce uses the OAuth protocol to allow users of applications to securely access data without having to reveal username and password credentials.
Twitter Sign-in - Works on websites, iOS, mobile and desktop applications.
Machine Learning
Amazon MI API - Amazon Machine Learning API simplifies the process of making predictions that require lots of expertise around model building, data cleansing and statistical analysis.
AYLIEN - AYLIEN Text Analysis API is a package of Natural Language Processing, Information Retrieval and Machine Learning tools for extracting meaning and insight from textual and visual content with ease.
Big ML - BigML is user-friendly and developer-friendly Machine learning API that mainly concentrates on decision trees.
IBM Watson - Simplifies the process of preparing data and makes it easier to run predictive analysis.
Microsoft Azure Machine Learning API - Helps data scientists publish in minutes which once used to take days after they had developed a feasible model.
Unplugg - Automated Forecasting API for timeseries data which can be used to forecast energy consumption, temperature, or any other timeseries data which has some seasonality effect.
Maps
Amazon Maps API v2 - Add interactive 3D maps, graphics, and custom overlays to your Fire Tablet and Fire phone apps.
Bing Maps - Bing Maps platform provides multiple API options for your application.
CartoDB - Allows you to generate maps based on data hosted in your CartoDB account.
Daum Maps API - Daum Maps provide multiple APIs for Korean map.
DigitalGlobe - DigitalGlobe Maps API delivers the world's best satellite imagery, straight to your app. #Beta
Infermedica - AI-based engine for patient triage and preliminary medical diagnosis. v2
Lexigram - NLP that extracts mentions of clinical concepts from text, gives access to clinical ontology. v1
Miscellaneous
Aadhaar Bridge - Aadhaar is a 12-digit unique identification number issued by the Indian government to every individual resident of India. API allows you to authenticate and perform ekYC and eSign using Aadhar. đź’¸
ApiLeap - Chrome based screenshot API to convert URLs & HTML to images.
Callook.info - Look up information about United States ham radio callsigns.
ChuckNorris.io - A free JSON API for hand curated Chuch Norris facts.
Domainsdb.info - Registered domain names search checks the lists of registered domains for names containing particular words/phrases/numbers or symbols.
FreeDB - Look up CD information using the freed database.
IP Sidekick - IP Sidekick is an API that returns information about an IP address. You can use it to customize your content based on the visitor's location or display their country.
JSONbin.io - Free JSON data storage service, ideal for small scale web apps, website, mobile apps.
LaunchLibrary - Aggregated info about space launches.
LetsValidate22 2 - Uncovers the technologies used on websites and URL to thumbnail.
LinkPreview - RESTful API that returns JSON formatted summary with title, description and preview image for any requested URL. Free & paid plans.
Marijuana Strain API - Documentation on over 2000 Marijuana strains including races, flavors, and effects.
Pastebin - Quickly share text or code, with support for over 250 languages for syntax highlighting.
Spreaker - Enables developers to read and write data to Spreaker.
StackExchange - The StackExchange API provides RESTful services to all the sites on the StackExchange domain.
RestCountries - Get information about countries via a RESTful API.
Who Hosts This - Detect the hosting provider powering any web site
WolframAlpha - Integrate top of the line computational knowledge into your applications through the WolframAlpha API. đź’¸
Wunderlist - The Wunderlist API provides REST-based storage and synchronization of a user’s lists across multiple platforms and devices.
Movies
OMDB - OMDb provides a subscription based web service to obtain information and metadata about movies. đź’¸
TMDb - TMDb provides powerful searches as well as powerful movie discovery.
Music
Deezer - Deezer API provides a nice set of services to build up web applications allowing the discovery of Deezer's music catalogue.
Discogs - Access database of artists, labels, releases, marketplace and more.
Last.fm - The Last.fm API allows anyone to build their own programs using Last.fm data, whether they're on the web, the desktop or mobile devices.
MuseScore - REST based API which provides music metadata.
musicApi83 20 - Centralized Node.JS API SDK for Xiami, Netease, and QQ music - The Top 3 music providers in China.
MusicGraph - Search through more than 7 billion music facts and connections.
NPR API - NPR's API is a content API, which essentially provides a structured way for other computer applications to get NPR stories in a predictable, flexible and powerful way.
QuantOneMusic - Answers the need for digital music data.
Rhapsody - Access metadata, user’s entire library of music and do much more.
SoundCloud - Using the SoundCloud API, you can build applications that take sound on the web to the next level.
Spotify - Spotify’s Web API lets your applications fetch data from the Spotify music catalog, manage users' playlists and saved music, get recommendations, control Spotify Connect, and more.
TheAudioDB - Free JSON API for music data, artwork, charting, ratings and hashes.
Music Analytics
Next Big Sound - API offers a very simple interface to access data from NBS. Ruby wrapper available.
Music Discovery
Rovi - Access to Metadata, search capabilities and recommendations.
Setlist.fm - The setlist.fm API has been designed to give you easy access to setlist data in order to build fancy websites and other applications.
TuneFind - Allows developers to enhance their services with song, show, and movie data from TuneFind.
Music Identification
Acoustid - Supports searching through their fingerprint database.
Gracenote - Largest source of music and video metadata on the planet.
Music Lyrics
ChartLyrics Lyrics API - Allows users to search for lyrics using the artist name, song title, or lyric text.
Lololyrics API - Given an artist and track name, obtains its lyrics and metadata such as the year released and album art. Specializes more in electronic dance music genres such as hardstyle.
Musixmatch - Power your music project by licensing access to the world’s most authoritative lyrics DB.
Music Stores
iTunes Search - The Search API allows you to place search fields in your website to search for content within the iTunes Store, App Store, iBooks Store and Mac App Store.
Faroo - Alternative to Google Web Search API / Google News Search API, allows you to search news within dates, fetch trending news, topics and terms.
New York Times - Article search, best sellers, campaign finance, community, most popular, real estate, movie reviews, NY state legislature, Times newswire, tags, people
NewsAPI - 70+ news sources and their headlines, one API.
The Guardian - Access a huge range of content from The Guardian.
Natural Language Processing
AlchemyAPI - IBM Company - Uses NLP and ML algorithms to extract semantic meta-data from content.
DialogFlow - Natural Language Interactions for Bots, Applications, Services, and Devices
Datum Box - Datumbox offers a powerful open-source Machine Learning Framework written in Java.
LUIS AI - Language Understanding Intelligent Service offers a fast and effective way of adding language understanding to applications.
MeaningCloud - Text analysis APIs for topic extraction, sentiment analysis, automatic classification, morphosyntactic analysis, language detection and more. Several languages are supported.
Open Calais - Good entity extraction, no sentiment analysis.
Recast.AI - Recast.AI provide an NLP API for text analysis and entity extraction. Recast.AI is the leading platform to build, connect and monitor bots.
Semantria - SAAS API based on Lexalytics engine. #Paid
TextRazor - Helps you extract and understand the Who, What, Why, and How from your supplied text. #FreeToUse
VoiceRSS - An API to convert Text to Speech, supporting 15+ major languages.
Wit AI - Provides an intent-based NLP API to easily build text and audio based chat bots.
Word Associations API - Provides service to get associations for a word or phrase. Words are grouped by semantics, meaning, and psychological perception.
Placeholder Images
DummyImage - Particularly nice, when compared to some of its competitors, in that it offers a great deal of flexibility.
Placehold - A quick and simple image placeholder service.
PlaceKitten - A quick and simple service for getting pictures of kittens for use as placeholders in your designs or code.
Satyr - Free powerful API for generating dummy images with unique features like delay, aspect ratio, variable resolution, themes, flags and offline mode.
Unsplash - Beautiful placeholders using images from the popular Unsplash
Places
CityGrid - Enables developers to create web and mobile applications that find local businesses, organizations, and points of interest by a variety of search criteria.
CountryAPI - Gets all the countries, and obtain the most important information of these.
Factual - Providing a places search that can be searched by latitude/longitude, and “where” using full text search query string.
Foursquare Venue - Providing a places search that can be searched by hierarchical list of categories, longitude/latitude etc.
Google Places API - Providing a places search that can be searched by latitude/longitude, keyword matched against all fields, name of place, type of place restricted by radius.
Nokia - Providing a JavaScript places search that can be searched by search term, with a detail search for display by JS widget.
Yelp - You can search location using longitude and latitude, neighborhood, address or city and filter listings by “where”, using a list of support categories.
YP - Providing a places search that can be queried by keyword and longitude/latitude, street address, city, postal code, Neighborhood, state, points of interest or by phone number.
Amazon Product Advertising API - Get access to the data used by Amazon including items for sale, customer reviews, seller reviews, item search, product promotions, and more.
Science
NASA - Get NASA data, including imagery, list of asteroids based on their closest approach date to Earth and much more.
Open Science Framework - A free, open source workflow/project management system for storing, collaborating on, and sharing research across the scholarly life cycle.
SHARE - A free, open dataset of scholarly research activity across the scholarly lifecycle.
Social Media
Daily Motion - Build applications centered around DailyMotion.
VK - Access to VKontakte's API. This has a variety of features such as authorization via VK, embedding VK comments for things like blogs, and taking payments via VK. Additionally, you may use the VK API to control much of the functionality on the website (for example, adjusting shop inventory in your VK community's market section).
Weibo - Programmatic access to China’s most popular microblogging site.
Whatsapp Document Interaction - If your application creates photos, videos or audio notes and you’d like your users to share these media using WhatsApp. #Limited
Po.st - Shorten URLs, Expand shortened URLs, see statistics etc.
Yourls - Generate or get existing short URLs, with sequential or custom keyword.
Videogames
Clash Royale140 53 - API that provides informations about Clash Royale game.
GiantBomb - API to query the GiantBomb database for videogames, characters, companies, genres and many more.
IGDB - Access the International Games Database and get information about videogames, characters, companies, genres and many more. Commercial usage is allowed.
TheGamesDB.net - Free API to access information about videogames, platforms, genres and ratings.
Weather
AerisWeather - Global weather data and imagery APIs, with a free developer subscription tier, boasting detailed documentation for simple to advanced queries, free SDKs and a Map Builder to get you up and running faster.
Forecast - The same API that powers Forecast.io and Dark Sky for iOS.
Open Weather - Access current weather data for any location on Earth including over 200,000 cities!
Weatherbit - Access forecasts, current weather, and historical weather data for any point on the Earth!
Weather Source - Powerful Weather API built for systems that demand speed, reliability and heavy load.
Wunderground API - Reliable data, accurate forecast, & global coverage in 80 languages.
Yahoo Weather API - Get up-to-date information for any location, including 5-day forecast, wind, atmosphere, astronomy conditions, and more.