- Original Keen Dreams source-code liberated
- Also check out: CloneKeen, Omnispeak & Commander Genius
- CaveExpress liberated (2d physics game)
- Pixel Dungeon RogueLike open-sourced (Android only)
- X-Com: Apocalypse engine reimplementation
- Libre content replacement project for Gish
- Stein's Gate Visual Novel Engine reimplementation
Big tease: Icculus works on open-sourcing a game and it seems to be a relatively new title as it includes steamworks support.
Please comment below if you know of other recent open-sourceing efforts ;)