The WordPress Codex is seeking volunteers for Codex Cleanup Week which is Saturday, June 18 through Sunday, June 26. This is a major push to clean up the Codex and stuff it full of great documentation so volunteers can relax a little this summer.
It is open to all WordPress users of every level who want to contribute to WordPress. There are tasks for the novice and experienced WordPress user, as well as for the novice to experienced MediaWiki user.
The WordPress Codex is the official online manual for WordPress users, currently packed with more than 350 articles on how to use, customize, and expand WordPress. The entire site is run and built by volunteers donating their time and effort to the WordPress Community through their editing and writing documentation.