These days I have been working in a small parser to convert BBCode to HTML in Ruby.
The motivation was that I need it (of course), and there wasn't anything complete enough. So I found bb-ruby at GitHub and I decided to complete it with more tags, tests, and some stuff for doing it more flexible.
The result is a fork that you can find here:
http://github.com/ferblape/bb-ruby/tree/master
You can read the README file for getting more information.
These is a tinymce mode that renders bbcode insted of html.
http://wiki.moxiecode.com/examples/tinymce/installation_example_1...
As you can see is so easy for the developper and the user