BlueCloth is a Ruby implementation of Markdown, a text-to-HTML conversion tool for web writers. To quote from the project page:
Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML).
BlueCloth 2 is a complete rewrite using David Parsons’ Discount library, a C implementation of Markdown. I rewrote it using the extension for speed and accuracy; the original BlueCloth was a straight port from the Perl version that I wrote in a few days for my own use just to avoid having to shell out to Markdown.pl, and it was quite buggy and slow. I apologize to all the good people that sent me patches for it that were never released.
This version offers several improvements over BlueCloth 1.x:
Passes all the tests in MarkdownTest 1.0.3.
Fixes all known bugs in BlueCloth 1.×.
It is several orders of magnitude faster than BlueCloth 1.x, and as fast or faster than any of the Markdown implementations for Ruby that I know about: