kramdown is yet-another-markdown-parser but fast, pure Ruby, using a strict syntax definition and supporting several common extensions.
The kramdown library is mainly written to support the kramdown-to-HTML conversion chain. However, due to its flexibility it supports other input and output formats as well. Here is a list of the supported formats:
input formats: kramdown (a Markdown superset), Markdown, HTML
output formats: HTML, kramdown, LaTeX (and therefore PDF)
All the documentation on the available input and output formats is available at kramdown.gettalong.org.
kramdown has a basic *Cloth API, so using kramdown is as easy as
require 'kramdown' Kramdown::Document.new(text).to_html
For detailed information have a look at the Kramdown::Document class.
MIT - see the COPYING file.