• Google Knol

    A Reference, encyclopedia, knowledge type of website
    http://knol.google.com/

• Wikipedia, The free encyclopedia

    A free and open online collaborative encyclopedia
    http://wikipedia.org/

• The Citizendium Compendium

    An open wiki project aimed at creating a large, free, and reliable encyclopedia.
    http://www.citizendium.org/

• Scholarpedia

    online wiki-based encyclopedia in which articles are written by invited expert authors and are subject to peer review.
    http://www.scholarpedia.org/

• How Stuff Works

    Learn how everything works
    http://www.howstuffworks.com/