PlanetMath is a free , collaborative, online mathematics encyclopedia . The emphasis is on rigor, 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.”. 
Was started PlanetMath 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 .
The main PlanetMath focus is on encyclopedic entries, and some forum discussions. In addition, the project hosts data about books, exhibitions 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 concept defined Within a more general entry.  An overview of the current PlanetMath happy est disponible.  About 300 Wikipedia entries incorporate text from PlanetMath articles Category: Wikipedia articles incorporating text from PlanetMath .
An all-inclusive PlanetMath Free Encyclopedia book of 2,300 pages is available for the encyclopedia. 
Content development model
PlanetMath implements a specific system called happy Creation authority model .  This is a set of rules which can add, modify or remove content. Only registered users can create or edit entries.
An author who starts a new article becomes its owner , who is the only person authorized to edit that article. Other users may add corrections and discuss improvements but the resulting modifications of the article, if any, are always made by the owner. However, if there are long lasting unresolved corrections, the ownership can be removed. More precisely, after 2 weeks the system starts to remind the owner by mail; At 6 weeks any user can “adopt” the article; At 8 weeks the ownership of the entry is completely removed (and such an entry is called “orphaned”).
To make the development more smooth, the owner may also choose to grant editing rights to other individuals or groups.
The user can explicitly create links to other articles, and the system also automatically turns certain words into links to the defining articles. The topic area of every item is classified by the Mathematics Subject Classification (MSC) of the American Mathematical Society (AMS).
The site is supervised by the Content Committee. Its basic mission is to maintain the integrity and quality of the mathematical content and organization of PlanetMath.  As defined in its Charter, the tasks of the Committee include:
- Developing / maintaining the standards for PlanetMath content
- Improving Individual PlanetMath entries in its Encyclopedia, Book, Paper, and Exposition)
- Developing topic areas
- Developing / improving site and user documentation
- Managing the PlanetMath Request List and Unproved Theorems list
- Improving categorization and other meta-attributes of entries.
- Developing software recommendations for improved content authoring and editorial functions.
PlanetMath happy is licensed under the copyleft Creative Commons Attribution / Share-Alike License . All content is written in LaTeX , a typeetting system, which is popular among mathematicians because of its support of the technical needs of mathematical typesetting and its high-quality output.
The software running PlanetMath is written in Perl and runs on Linux and the Apache web server . It is known as Noosphere and has been released under the free BSD License . As of March 13, 2013 PlanethMath has retired Noösphere and runs now on a software called Planetary , which itself was implemented with Drupal .
Encyclopedic content and bibliographic materials related to physics, mathematics and mathematical physics are developed by PlanetPhysics . The site, launched in 2005, uses similar software (Noosphere), aim a.  Additionally, a PlanetComputing project is envisaged that would also include Computational Physics and AI together with logical, categorical, ontological and mathematical foundations of computers and automata. (Seems to be abandoned plan.)
- List of online encyclopedias
- Jump up^ Self-descriptions of PM “Archived copy” . Archived from the original on 2016-08-26 . Retrieved 2009-05-15 . , “Archived copy” . Archived from the original on 2016-06-11 . Retrieved 2008-05-02 . “Archived copy” . Archived from the original on 2008-05-09 . Retrieved 2009-05-19 .
- Jump up^ “PlanetMath Encyclopedia” . Archived from the original on 2013-02-15.
- Jump up^ “Overview of the content of PlanetMath” . Planetmath.org. 2013-03-21 . Retrieved 2013-09-06 .
- Jump up^ PlanetMath “ Free Encyclopedia ” book ArchivedJune 20, 2016, at theWayback Machine. Based on 2004-2005 content of PlanetMath
- Jump up^ Noosphere’s ArchivedMarch 4, 2016, at theWayback Machine. Authority model
- Jump up^ Username *. “ContentCommittee Charter” . Planetmath.org . Retrieved 2013-09-06 .
- Jump up^ PlanetPhysics.org ArchivedFebruary 25, 2009, at theWayback Machine.
- Jump up^ Free Book downloadsin PDF format, Original Papers (~ 10 pages) and Exhibitions (> 30 pages)[ dead link ]