Just for completeness' sake I have gone over Wikipedia's list of lightweight markup languages and added support in Nikola (a static site and blog generator) for a couple of them: BBCode and txt2tags, which brings the number of supported markup formats to 7 (the others are reStructured text, markdown, HTML, textile and Wiki).
Of the list of markup languages, the only missing ones with a Python implementation are AsciiDoc and Markdown Extra.
Why bother with this? It's not as if there was someone asking for BBCode support. However, one of the uses I want to support is archiving sites. Suppose you have a forum you want to shut down? I want you to be able to archive it (even if it's some work) and keep the data out there. A wiki? Same thing.
This is a first step in that direction.