Nikki and the Robots is an incredibly cute platformer developed by people with exotic taste for revision control [Darcs repo] and programming language (Haskell). Read more on joyride's code page. There's a nikki wiki and a bug tracker.
A story mode is in development, which will be proprietary and for-pay.
Code is under LGPL and free-version-art under CC-BY-SA.
I made a little level pack: