"FLTK (pronounced "fulltick") is a cross-platform C++ GUI toolkit for UNIX®/Linux® (X11), Microsoft® Windows®, and MacOS® X. FLTK provides modern GUI functionality without the bloat and supports 3D graphics via OpenGL® and its built-in GLUT emulation."
"U++ is a C++ cross-platform rapid application development framework focused on programmers productivity. It includes a set of libraries (GUI, SQL, etc..), and an integrated development environment."
"Allegro is a game programming library for C/C++ developers distributed freely, supporting the following platforms: DOS, Unix (Linux, FreeBSD, Irix, Solaris, Darwin), Windows, QNX, BeOS and MacOS X. It provides many functions for graphics, sounds, player input (keyboard, mouse and joystick) and timers. It also provides fixed and floating point mathematical functions, 3d functions, file management functions, compressed datafile and a GUI."
Bloodshed Dev-C++ is a full-featured Integrated Development Environment (IDE) for the C/C++ programming language. It uses Mingw port of GCC (GNU Compiler Collection) as its compiler. It creates native Win32 executables, either console or GUI. Dev-C++ can also be used in combination with Cygwin.
The Visual Component Framework is an advanced C++ application framework that makes it easy to produce powerful Windows applications in C++. The framework is a based on a thoroughly modern C++ design and has built in support for Rapid Application Development (RAD). The framework is designed to be portable over multiple platforms and compilers, so you don't have to lose all that work that went into writing your app for a single platform!
"wxDev-C++ is an extension of Dev-C++ by Colin Laplace et. al. This program helps you to create dialogs and frames for wxWidgets visually using a form designer. With all the wonderful features of Dev-C++, wxDev-C++ is still being actively developed. The main aim of this project is to provide the wxWidgets community with a free, open-source, commercial-grade IDE/RAD tool for development with wxWidgets."
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wxWidgets lets developers create applications for Win32, Mac OS X, GTK+, X11, Motif, WinCE, and more using one codebase. It can be used from languages such as C++, Python, Perl, and C#/.NET. Unlike other cross-platform toolkits, wxWidgets applications look and feel native. "