There’s a markup language called Creole. I came across it while installing the Gems for Gollum and Markdown. It’s home page notes that it’s for translating documents between various wiki markups, but it looks pretty useful all by itself. I particularly like that it uses has symbols, `#`, for numbered lists and the more commonly used equal signs, `=`, for headings. If I could change one thing about the Markdown conventions that would be it.
Well, I would change a number of things about the Markdown convention, but that’s for another note. I should note that I am free to do so thanks to [John Gruber’s generosity][md] and that there are a lot of people who have done amazing things with Markdown, like [Fletcher Penney][mmd] and [Michel Fortin][php] — and I depend upon both their implementations on a daily basis — but such a fundamental shift as `# -> =` would seriously affect a rather significant amount of work I already have “formatted” in Markdown.