Here’s my entry to the contest. And here’s the code. Besides the basic markdown syntax, I cover Github and Reddit extensions.
The site has two sections. The first is a reference sheet for the three versions covered. The second is the interactive tutorial. It’s heavily based on Garen Torikian’s tutorial, adding a few things and putting it together with a bunch of jquery plugins to speed up development. There’s a challenge at the end of the tutorial that now that I see it I don’t know if I got it right. Anyway, I hope it helps someone, any kind of feedback is welcome.