Before Valve began greenlighting games by the bucketload, busting onto Steam was seen as a massive accomplishment for an indie developer. So it always raises one's curiosity when a game's creator decides to leave the berth of the all-mighty digital distributor for the lands of open source. In this case, it's Richard Hofmeier and his IGF prize-winning title Cart Life.
According to Rock, Paper, Shotgun's Graham Smith, Hofmeier decided to pull the plug (and stick it into another socket) because he was "done supporting it / fixing bugs" and it was "time to stop charging & open it up (despite fears of code nakedness)". So, rather than charge for it on Steam, he made the decision to open up the code and let enterprising players patch problems and, potentially, create their own variations of the game.
Unfortunately, Hofmeier's site is currently down, so if you were planning on checking out Cart Life's innards, you'll have to wait until the rest of the internet has finished smacking the packets out of it.