- PlanetMath.org — Math for the people, by the people.
PlanetMath originally used the "Noösphere" software, which was written especially for PlanetMath. However, some would argue that "Noösphere" has diverged enough from more traditional wiki that it is no longer a wiki engine. The Noösphere wiki content was originally released under the GNU Free Documentation License, but this was subsequently changed to the Creative Commons Attribution 3.0 United States License
In March 2013, a new version of the PlanetMath wiki has been released on the new developmental Planetary wiki engine. Its content is released under the Creative Commons Attribution-Share Alike 2.0 license.
See also the related wiki: AsteroidMeta.