Qt Bug Tracker - If you think you've found a bug with Qt or one of its related projects, report it here (or see if someone else already has).
Qt Code Review - See how the Qt maintainers ensure their code is well-written.
Source Code - Browse the various source trees that comprise the Qt project. Has mirrors at several GitHub organizations:
If you build it, they will come. This section describes aggregations of Qt users who share knowledge and code with one another. The most popular and active communities are listed in this section, but you can find a more comprehensive list here (that includes several in other languages) if you'd prefer.
Mailing Lists - Mailing lists for users and developers of Qt alike. Arguably the best place to communicate directly with Qt's maintainers. Sees frequent activity.
Qt Forum - If e-mail's not your thing, then you might also consider getting help or sharing knowledge on the forums.
Qt Wiki - The premier source for user-contributed Qt knowledge.
IRC - For real-time chat with other Qt developers and users. The most popular channels are on Freenode, and include #qt, #qt-quick, #qt-creator, and #qt-chat.
For a full list of Qt-related IRC channels, see here.
Note that the linked webchat client is not a part of the Qt project, and is provided by the author of this list for convenience only. These channels can be accessed through any IRC client.
A good developer writes his or her own tools. A great one uses tools others wrote. This section will help you be great; more formally, this section details applications that make it easier to create software with Qt. You may also be interested in the Libraries section.
The Qt framework has surprisingly many tools that don't get the spotlight. This section describes them (as well as the star players that do). For the purpose of this section, "tool" refers to Qt-centric utilities whose code does not get embedded within your application (but their output might).
Qt Creator - By no means does Qt lock you into its provided IDE, but its firm integration with the framework makes it a good sell. Among other things, it provides a UI designer, modeling tools, a documentation browser, and great QML support if you're into that sort of thing. There's also a plugin system, but third-party plugins are unfortunately scarce.
Qt Designer - If you'd rather just design the interfaces and let someone else hook them up to logic, the GUI designer is available as a separate application.
Qt Assistant - So is the documentation viewer, for that matter.
Qt Linguist - Qt provides excellent internationalization/localization support, and this tool is very much responsible for it. Write translatable strings in your code with special macros, and this tool will aggregate them all for you so you or your translator(s) can broaden your software's audience.
Qt Installer Framework - Nobody seems to talk about this, but Qt also provides a way to write an installer for your application. Does not support creation of macOS disk images, app bundles, or Linux packages, so be mindful of that when considering your project's distribution.
macdeployqt - Generates macOS application bundles for Qt projects.
qmake - The bundled build system designed for Qt, though it can be used for non-Qt projects.
qbs - If QML is more your style, consider this alternative build system.
Emulator - Don't forget about Qt's mobile support!
qtdiag - Command-line tool that prints out a lot of information pertaining to both your Qt installation and your system in general. No link because there's no dedicated web page; just run qtdiag on the command line. Excellent for troubleshooting.
qmleasing - Lets you make easing curves suitable for QML, though if you understand the underlying math there's no reason you couldn't use the resulting numbers elsewhere.
CMake - General C++ build tool that happens to have great Qt support.
GammaRay - Powerful debugger and general inspection tool for Qt-built software. Lets you inspect and manipulate the QObject hierarchy, view object properties, edit widgets at runtime, and far, far more. A two-sentence blurb can't do it justice, seriously check it out.
moc-ng55 7 - Alternative implementation of moc that's binary-compatible with Qt's version.
Qt-Inspector48 3 - Inspection tool with similar goals to GammaRay, though much simpler.
SIP📦 - Generates Python bindings for C or C++ libraries. Has special support for Qt signals and slots, and was used to create PyQt.
linuxdeployqt311 77 - Lets you bundle your Qt based application as an AppDir or AppImage, making it possible to ship it to users of many desktop Linux distributions. Similar to the official windeployqt and macdeployqt tools but for Linux.
Bindings in Other Languages
This section describes software that enables creation of Qt software in a primary language other than C++. Libraries that allow run-time scripting in a Qt application are listed under Integrations.
Python (via PyQt)📦 - Arguably the most comprehensive and well-known binding of Qt to another language.
Python (via PySide)📦 - Another binding for Python, which has been officially adopted by the Qt project.
This section describes two kinds of third-party libraries; those that provide their own brand-new functionality (e.g. widgets, dealing with particular file formats), and those that provide integrations with existing software (e.g. scripting languages, clients for REST APIs, implementations of established protocols).
For the purpose of this section, an "Integration"-focused library does one of the following:
Serves as a client for an established Web service.
Wraps another library in a Qt-friendly manner as more than just an implementation detail (i.e. it tries to mimic the wrapped API).
QScintilla📦 - Absurdly versatile and customizable text editor widget that provides syntax highlighting, code completion, code folding, recordable macros, and much more. Built around Scintilla. Created by the same company that developed PyQt.
QtLua📦 - Use Lua as a scripting language for Qt-based software.
qtruby - Use Ruby as a scripting language within your application.
QuaZIP📦 - Read from and write to ZIP archives. Uses Minizip under the hood.
VLC-Qt - Wrapper for libvlc that lets you add a VLC-like media player to your application.
Communi - Cross-platform IRC framework. We've got enough IRC clients out there already, but I suppose this could also be used to implement a chat function in your application (e.g. for community support).
cutelyst - Web framework that takes some ideas from Perl's Catalyst framework.
DiceParser5 2 - Dice Roller framework based on its own syntax.
DOtherSide91 23 - Binding for QML in C, primarily designed as an API for other languages to support QML.
glraw18 6 - Convert images from any Qt-supported format to OpenGL-format textures. Useful for speeding up texture loading in graphics applications.
QtVerbalExpressions4 0 - Create regular expressions using natural English expressions. Part of the VerbalExpressions project, which does the same thing for a wide variety of languages.
qtwebserver - If you need to write a web application server in Qt for some reason, this'll help you along.
QtXlsx - Read and write spreadsheets in Microsoft Excel format.
Qwt📦 - Qt widgets designed for scientific and technical applications.
V-Play - Cross-platform 2D game engine and app framework that relies heavily on QML. Has a lot of tools and resources, and may even deserve its own list.
verdigris120 7 - Experimental library to write Qt applications without using the moc.
If the Libraries section doesn't satisfy you, perhaps one of these will.
#inqlude - The most well-known aggregation of Qt-centric libraries out there. A package manager is also available here.
QtPods - Another Qt-centric package manager. If you want to see the offerings without using QtPods, the full list is available here, and can be added to by submitting a pull request.
Linux-Apps.com - Despite the name, Linux-Apps.com aggregates a wide variety of Qt-based tools and libraries for both end-users and developers.
Stephan Binner's Ubuntu PPAs - Ubuntu users who are hesitant to install anything outside of their package managers can obtain any recent version of Qt from these repositories. Instructions for adding them are found within.
Each entry is followed by a standout list of articles, talks, or other resources.
Planet Qt - Official aggregation of first-party and third-party Qt-related blogs.
ICS - Qt-centric software consulting firm with a really neat blog. Specializes in graphics applications.
Qt Tips and Tricks [1, 2] - Odds and ends that might be nice to keep in your back pocket.
Mastering Qt File Selectors - Sometimes you need different variations of the same asset, but you won't know which ones to load until runtime. This class will decide for you.
Some Lesser Known Qt Tools and Commands [1, 2, 3, 4, 5] - You don't find hidden gems by staying on the beaten path.
There's also an official showroom here, which lets developers submit their own Qt-powered applications for display.
Other Relevant Awesome Lists
If you're familiar with Awesome, you'll know that there's an extremely wide variety of resources, the usefulness of which will depend on your project. However, if you're developing Qt applications, you'll almost certainly want to look at these as well.
Awesome C/C++2k 326 - There's no reason you can't use C++ libraries that weren't designed for Qt. Sometimes they might even suit your needs better than what Qt offers.
Awesome C556 69 - Same goes for C libraries; might wanna brush up on those RAII techniques while you're at it.
Awesome CMake651 45 - If you're not using qmake for your project, you're likely using CMake instead.
Awesome OpenGL526 66 - Qt is commonly used for graphics applications, even providing its own wrappers around OpenGL.
To the extent possible under law, Jesse Talavera-Greenberg has waived all copyright and related or neighboring rights to this work. See the LICENSE file for details.