Pycraft is an open-source, OpenGL based game made in Python
GemRB is a portable open-source implementation of the Infinity Engine
Vivid3D is a C++ IDE/3D engine, with python scripting.
A game engine for console based text games
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Tactical, turn-based game engine, that uses OpenGL and WinAPI
Open source, moddable game engine for the "Polygon Love 2" game