peg-multimarkdown is a fork of John MacFarlane's peg-markdown, a Markdown parser written in C using a parsing expression grammar (PEG). It adds support for MultiMarkdown, and will become MultiMarkdown 3.0 when finalized - replacing the original Perl version.
This wiki contains the new User's Manual for MultiMarkdown 3.0. It's still in progress, and I welcome contributions.
I no longer plan to rewrite everything to move away from glib2 since it's proven to be fairly easy to put that on any OS. That said, however, it should be pretty easy to migrate towards a pure Cocoa approach for Mac OS X which would also open up iOS development. humblehacker has done this for peg-markdown, so it's definitely possible.