GTK is described as 'Multi-platform toolkit for creating graphical user interfaces. Offering a complete set of widgets, GTK is suitable for projects ranging from small one-off tools to complete application suites' and is a popular app in the development category. There are more than 25 alternatives to GTK for a variety of platforms, including Windows, Linux, Mac, Android and Self-Hosted apps. The best GTK alternative is Qt, which is both free and Open Source. Other great apps like GTK are Flutter, Electron, PyQt and Avalonia UI.
Qt is a cross-platform application framework that is widely used for developing application software that can be run on various software and hardware platforms with little or no change in the underlying codebase, while having the power and speed of native applications.
Most users think Qt is a great GTK alternative.
Build apps for any screen. Flutter transforms the app development process. Build, test, and deploy beautiful mobile, web, desktop, and embedded apps from a single codebase.
GTK is C based for desktop apps on non-mobile OS:es, Flutter is designed for mobiles.
If you can build a website, you can build a desktop app. Electron is a framework for creating native applications with web technologies like JavaScript, HTML, and CSS. It takes care of the hard parts so you can focus on the core of your application.
Avalonia is a WPF-inspired cross-platform XAML-based UI framework providing a flexible styling system and supporting a wide range of platforms including: Windows, Linux (desktop & embedded), macOS, Android, iOS and Browser.
I like Avalonia, but it is not an alternative to GTK+. Avalonia is dotnet, GTK+ is not integrated with dotnet, it is an independent C library.
The Qt for Python project aims to provide a complete port of the PySide module to Qt.
Photino is a lightweight open-source framework for building native, cross-platform desktop applications with Web UI technology.
wxWidgets is a C++ library that lets developers create applications for Windows, OS X, Linux and UNIX on 32-bit and 64-bit architectures as well as several mobile platforms including Windows Mobile, iPhone SDK and embedded GTK+.
full features, nice architecture
Uno is the platform for building native mobile, desktop and WebAssembly apps with C#, XAML from single codebase. It's a Universal Windows Platform Bridge that allows UWP-based code (C# and XAML) to run on iOS, Android, and WebAssembly.
gtkmm is the official C++ interface for the popular GUI library GTK+. Highlights include typesafe callbacks, and a comprehensive set of widgets that are easily extensible via inheritance. You can create user interfaces either in code or with the Glade User Interface designer...
wxPython is a GUI toolkit for the Python programming language. It allows Python programmers to create programs with a robust, highly functional graphical user interface, simply and easily. It is implemented as a Python extension module (native code) that wraps the popular...
Finland
EU
United States
Estonia
Canada
GTK + and QT are the two major players that dominate the Desktop Environment on GNU / Linux today.