While it is just another classic overhead-scrolling space shooter, it is a game with a twist. You can not let any of the alien ships past you; each one will cost you a life. Moreover, the ammunition is also limited. This is what makes the game very challenging, almost impossible.
The idea is simple. You have to keep building walls and outrun your opponent by not bumping into either your wall or your opponents. While the game has options of playing against the bot, the game truely shines when it is played against a number of human players (LAN or online).
Frets on Fire is an open source clone of the ever-popular PlayStation 2 music/rhythm game Guitar Hero. It’s a free download and is available for Windows, Linux and the Mac, though the Mac version is experimental.
Hedgewars is multiplatform, a free turn-based blast-em-up in the vein of Worms. It features a wide range of weapons, multiple maps, and excellent graphics and audio. Offers single player, multiplayer, and (in theory) multiplayer over the internet modes.