An extensively hyperlinked collection of facts, ideas, notes and humor to which anyone can add.

A volunteer-run open content encyclopedia.

Collaborative, peer-reviewed mathematics encyclopedia with TeX input, inspired by MathWorld (GNU Free Documentation License).

Nupedia was a public peer-reviewed general encyclopedia created by volunteer scholars, with resources for readers and contributors (GNU Free Documentation License). It can be considered to be Wikipedia's direct ancestor.

A collaborative project of the DailyKos community to build a political encyclopedia.

A directory of people, organizations and issues shaping the public agenda. It catalogs PR firms, activist groups and government agencies as well as the criticisms that are made of these groups from different perspectives.

Wiki with stricter editing rules and obligatory disclosure of editor's real names.

A peer edited Star Trek encyclopedia.

The engineering, theoretical concepts, and organizations of the Internet (freely distributable).

A collaborative music encyclopedia. Contains melodies and musical themes from classical, popular, and folk music. Can be searched based on the melody alone, either by playing it on a keyboard, whistling or singing, or by entering the melodic contour a...