I suppose this might be similar to this question, but I'm wondering if there's a standard/popular mark up language for wiki and similar style user provided content. With the proliferation of different mark up syntaxes out there it seems like one would be a defacto one to implement. There appears to have been at least one group that wanted to create a standard (and an RFC for it), but they appear to have fizzled out around mid-2005.
So does anybody know what the standard/most popular one is? If there isn't one, what's the easiest for users but has a good flexibility for advanced users?
Markdown is popular in some circles. In addition to the original version in Perl, there's a C version called Discount and several other implementations including one in Lua.
There's a list of lightweight markup languages here.