An interesting new title called The Castle Doctrine, by indie dev Jason Rohrer, has just entered into alpha, and it's also now available to buy. The game is currently $8/£5.28 (half of its eventual price) and can be purchased direct from the game's website.
It's a massively multiplayer game of burglary and home defence, with the aim of the game to invade other people's virtual homes, whilst keeping yours secure and safe from home invasion.