Textile
From Just Solve the File Format Problem
Textile is a text markup format with the file ending of .textile. It is made to be rendered to HTML. Textile supports simple markup for things like: Emphasized text, Lists, Tables, Code, Headings, Blockquotes, Notes, Links, Email links, and Images. Textile is released under a BSD-style license. It is used by companies such as 37signals, and has rendering implementations in python, ruby, javascript, php and perl.
