Jason Rohrer, the developer behind games like Passage and Diamond Trust of London, has released the alpha build of his newest game, The Castle Doctrine. Rock, Paper, Shotgun has a good two-part preview that details how the game plays.
The basic gist is that you must set up your home with various traps and guard animals to protect your family and what little wealth you have left. After you've done that, you are free to invade other players' homes, in an attempt to circumvent their home defenses and steal their money, with which you will buy more traps for your own home. It's a vicious cycle.
If you want in now, you can get an open-source, DRM-free copy for eight dollars, with access to all future updates. If you'd prefer to wait until after the alpha phase, that price will double.
Impressions, Part 2: Jason Rohrer's The Castle Doctrine [Rock, Paper, Shotgun]