Enigma is a puzzle game
GemRB is a portable open-source implementation of the Infinity Engine
Orx: Portable Game Engine
A free transportation simulator game
RTS game with the theme of Strategy by Design
A strategy game with a high fantasy theme
A modern, cross-platform Quake game engine based on FitzQuake.
A cross-platform port of Hexen II game.
Seven Kingdoms: Ancient Adversaries
Odamex is a free, cross-platform, modern client-server Doom engine
Cross-platform, GPL reimplementation of the classic : Syndicate
Vtech Creativision and clones. CSL, Salora Manager, Laser 2001
Cross-platform real-time strategy game (3D)
SDL based generic 2D game engine
Old style soccer game with many exciting features
a (simple) Sokoban game