[1] 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.

Other users may add corrections and discuss improvements but the resulting modifications of the article, if any, are always made by the owner.

PlanetMath originally used software written in Perl and running on Linux and the web server Apache.

PlanetMath retired Noösphere in favor of another piece of software called Planetary, implemented with Drupal.

The site, launched in 2005, uses similar software (Noosphere), but a significantly different moderation model with emphasis on current research in physics and peer review.