The Mozilla Developer Center
The Mozilla Developer Center (affectionately known as Devmo) is one of web development’s best kept secrets. The site describes itself as
a Mozilla project dedicated to providing documentation, education, and community for developers of all types. What that means is extensive articles and tutorials on a wide range of important techniques – Ajax, CSS, SVG and much, much more.
Behind the scenes, the site is running a beautifully templated version of MediaWiki – the best-of-breed wiki software originally developed for Wikipedia. Registration is required before you can contribute, but there’s plenty to do if you can spare some time for the project. The site has a small but active community, and the quality of the content is extremely high. Well worth exploring.