DayZ - DayZ is an open world multiplayer survival game that tosses you in the midst of a zombie apocalypse.
Lexica - An open source word-search game.
7 Days to Die - 7 Days to Die is a post-apocalyptic survival game, during which players must craft shelters and horde resources in order to survive waves of undead enemies. Read more about 7 Days to Die.
Crosswords Arena - Word game, multiplayer and computer players
Project Zomboid - The Ultimate Zombie Survival RPG.
Quackle - Open-source word game similar to Scrabble. Features a board editor, analysis tools, and artificial intelligence that rivals the best players in the world!