OpenXcom

SuperTux source code

Clone of the Age of Empires II engine

Cataclysm - Dark Days Ahead. A turn-based survival game set in a post-apocalyptic world.

Space exploration, trading, and combat game.

Open-source engine for Heroes of Might and Magic III

Widelands is a free, open source real-time strategy game with singleplayer campaigns and a multiplayer mode.