PlanetMath

PlanetMath is a free, collaborative, online mathematics encyclopedia. The emphasis is on rigour, openness, pedagogy, real-time content, interlinked content, and also community of about 24,000 people with various maths interests. Intended to be comprehensive, the project is currently hosted by the University of Waterloo. The site is owned by a US-based nonprofit corporation, "PlanetMath.org, Ltd".

PlanetMath was started when the popular free online mathematics encyclopedia MathWorld was temporarily taken offline for 12 months by a court injunction as a result of the CRC Press lawsuit against the Wolfram Research company and its employee (and MathWorld's author) Eric Weisstein.

Content

The main PlanetMath focus is on encyclopedic entries, and some forum discussions. In addition, the project hosts data about books, expositions and research-level (not necessarily published) papers. A system for semi-private messaging among users is also in place.

As of 15 February 2013, the encyclopedia hosted about 9,289 entries and over 16,258 concepts (a concept may be for example a specific notion defined within a more general entry. An overview of the current PlanetMath contents is also available. About 300 Wikipedia entries incorporate text from PlanetMath articles Category:Wikipedia articles incorporating text from PlanetMath.