Apps similar to Agar include Qt, which is open source with a free version. Other options are Qt Creator, GTK, wxWidgets and PyQt. You can choose from more than 10 Software Frameworks like Agar for Linux, Mac, Windows, Android and iPhone.
The Standard Widget Toolkit (SWT) is an open source widget toolkit for Java designed to provide efficient, portable access to the user-interface facilities of the operating systems on which it is implemented.
United States
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...
Nana C++ Library takes aim at easy-to-use and portable library, it provides a GUI framework and threads for easy programming with modern C++ methods, such as traits, metaprogramming and other template technologies. .
Nevron Open Vision for .NET is a suite of advanced UI components that helps you develop feature-rich Web (Blazor WebAssenbly) and Desktop (WinForms, WPF, Xamarin.Mac) applications from a single code base.
Bulgaria
EU
IUP is a multi-platform toolkit for building graphical user interfaces. It offers a simple API in three basic languages: C, Lua and LED. IUP's purpose is to allow a program source code to be compiled in different systems without any modification.
PyGTK lets you to easily create programs with a graphical user interface using the Python programming language. The underlying GTK+ library provides all kind of visual elements and utilities for it and, if needed, you can develop full featured applications for the GNOME Desktop.
The FOX toolkit is an open source, cross-platform widget toolkit, that is, a library of basic elements for building a graphical user interface (GUI).
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