This month there's been the Humble Indie bundle
whereby anyone can purchase this game bundle consisting of World of Goo, Aquaria, Gish, Lugaru, and Penumbra Overture for any price they want. Part of the proceeds would be donated to the Electronic Frontier Foundation and Child's Play Charity. With the success of this bundle, they then decided if they generate more than a million dollars in revenues they would open-source the games. Well, they have achieved this milestone!
Aquaria, Gish, Lugaru HD, Penumbra Overture are now being open-sourced thanks to the success of the Humble Indie Bundle. Lugaru HD is already opened up and the other games are on the way. Unfortunately it doesn't look World of Goo is being open-sourced at this time.
Details on this work and these Linux-compatible games being open-sourced, check out the Wolfire blog