The most often used are Qt and GTK+ / co (gtkmm / *mm for C++ OO bindings), WxWidgets and FLTK (toolkit only) are also around. Take a look their online docs. For more "Full" framework then mass of cooperative libraries, look at Qt and WxWidgets. When it comes to quality of software documentation, Qt, Vim, and OpenBSDs manuals are the best I've seen, but only Qt is a framework \o/.
Stargella is a game meant to be in the same spirit as
Galaga/
Galaxian, and share as much of the code base with a tactical shooter, and a mech combat game that are each 'next up'. While it originally began as a C++/OGRE project, however portability requirements have caused me to code from scratch using plain C and OpenGL. Since it's never left my LAN, all the documentation is here too lol.
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Journal
Thou shalt check the array bounds of all strings (indeed, all arrays), for surely where thou typest ``foo'' someone someday shall type ``supercalifragilisticexpialidocious''.