Platforms: PC, Mac (uses MS Silverlight) - - Now (mostly) playable on Linux!
Distribution: Direct download, Desura, browser-based (website, Facebook, Kongregate)
atWar, formerly Afterwind, is an online multiplayer turn-based strategy game. In the best traditions of Risk and Axis & Allies, you play against other people to fight for world domination. Features free unit movement - no grids or predetermined paths. Up to 20 players in a game, simultaneous turns. Another feature is the Map Editor allowing players to create their own maps and units, giving you the chance to re-enact any battle real or imagined.
I finally got around to trying out the free version of this yesterday. I'm not usually big on strategy games, but atWar struck me as very well made, and the sense of scale you get from the globe-spanning battles is huge. The game also supports tons of user editors and stuff for creating custom maps, scenarios, and even units for your games. Want to play the Jedi fighting the Sith across the galaxy? Go ahead and make it. Want to battle IndieGameStand against bundle giants like Humble and Groupees? You can probably make that too.
The game has a free version, but the premium edition is what allows you to create custom content, among other things. I think it would be pretty sweet if we could get it featured here. The community is already pretty strong though, and the devs might not want to drop the $40 full-premium price for a sale here.