Markup Languages

Electronic Documents Markup
A brief explanation of what markup languages are and where they come from.
http://web.cs.wpi.edu/~kal/elecdoc/EDmarkup.html

Microformats
Simple data formats built upon existing and widely adopted standards. Overview, specifications, events, and discussion.
http://microformats.org/

Project Xanadu
The original hypertext project. Includes a history of the project and gives credit to the early developers of markup languages.
http://www.xanadu.com/

YAML Ain't Markup Language (YAML)
A straightforward machine parsable data serialization format designed for human readability and interaction with scripting languages such as Perl and Python.
http://yaml.org/