OptFrame is a framework for efficient implementation of metaheuristics and optimization methods. It has already been used in some real combinatorial problems and applied to Operations Research. Since November 2017, project has been moved to GitHub (new releases will also be included here in SourceForge, but Git mainline is no longer supported here). For more information, visit: https://github.com/OptFrame/optframe
A cross-platform GUI library
wxWidgets is a C++ library that lets developers create applications for Windows, Mac OS X, Linux and other platforms with a single code base. It has popular language bindings for Python, Perl, Ruby and many other languages, and unlike other cross-platform toolkits, wxWidgets gives applications a truly native look and feel because it uses the platform's native API rather than emulating the GUI. It's also extensive, free, open-source and mature.
Forge Flex is a Game Engine supporting isometric maps, graphics (shapes, images, fonts, sprites) audio and interface components wrote in C++, using DirectX.