Minecraft is a fun arcade game where you explore lost worlds, kill monsters and uncover secrets. Download here for Windows, Mac and Linux. This is the Frostburn Update.
Minetest is an infinite-world block sandbox game and a game engine, inspired by InfiniMiner, Minecraft and the like. It has been in development and use since October 2010.
Software that can be used as an alternative to Ace of Spades: