I miss the Eudyptula Challenge [0], I never got around to complementing it. It was a series of 20 challenges to introduce you to Linux kernel development, and it was done entirely over email. I think it's been shut down for a few years now, I'm not sure when or if it'll come back at this point.<p>[0] <a href="http://eudyptula-challenge.org/" rel="nofollow">http://eudyptula-challenge.org/</a>