Ace of Spades is a new free to play multiplier only FPS. Right now it is only in beta but the lack of features is actually quite refreshing.
The basic premise is a FPS in a complete sandbox environment made of Minecraft style blocks. These blocks can be added and removed with relative ease allowing you to create buildings and fortifications while at the same time you and your team must protect your intel (flag) from the enemy team and try to steal their intel as well.
At this point, beta .51, you are equipped with a simple offensive load-out; You have your trusty bolt action rifle and some grenades. The biggest issue I have with the game is that while the combat with these weapons is fun, it is mostly useless as only capturing the lintel matters and enemies re-spawn almost instantly. In fact I have never seen an example of intel ever being captured under regular circumstances, and it basically is impossible, as far as I can tell, if both teams have a moderate amount of members and no one is cheating.
Still the game can be an interesting diversion and only promises to get better, so if you want to check it out go to ace-spades.com (note: it is a download game but you start a game by clicking on one of the active servers in the list on the webpage, I recommend aloha uswest pinpoint).
It is not a particularly photogenic game, but pictures can be seen at the official Ace of Spades Gallery.