From Wikipedia, the free encyclopedia.
Open content, coined by analogy with open source, describes any kind of creative work (for example, articles, pictures, audio, video, etc.) that is published under a non-restrictive copyright license and format that explicitly allows the copying of the information. (An example is the GNU Free Documentation License, which is used by Wikipedia and Nupedia.) "Open content" is also sometimes used to describe content that can be modified by anyone. Of course, this is not without prior review by other participating parties--but there is no closed group like a commercial encyclopedia publisher which is responsible for all the editing.
Just as open source software is sometimes described simply as Free Software (not to be confused with Freeware), open content materials can be more briefly described as free materials. But not every open content is free in the GNU GPL sense (for instance the Open Directory). Some licenses attempt to maximize the freedom of all potential recipients in the future, while others maximize the freedom of the initial recipient. See public domain, free content, free software movement, copyleft.
Open content projects (in alphabetical order):
- Aozora Bunko (in Japanese) - free digital Japanese books
- Asian Open Source Centre  - contains an open content GFDL wiki on open source 
- BerliOS 
- Bitzi - free community-built catalog of digital files
- California Open Source Textbook Project  - K-12 textbooks and other curriculum materials
- Common Content  - open catalog of Creative Commons licensed content
- Connexions Repository  - Rice University's course material
- Creative Commons
- Eldritch Press  - books
- ExtinctionLevelEvent.com - Open Content Web Comic 
- FreeMedia  - stock photos from the University of North Texas
- Jake  - Research software and database where content is built in an open source way
- GNUtemberg  in Italian.
- ibiblio 
- Libre Society  - open culture site
- Linux documentation project  - Content project to develop documentation for Linux
- LOCA_Records  - open content record label
- Magnatune  - open content record label
- Nupedia  - peer-reviewed encyclopedia
- Opart  - Open art pool
- Opencode  - consortium for open research and content
- OpenContent  - open source licensing scheme for information content
- Open Content for Education 
- Open-education.org  - Portal and advocacy-site for collaborative creation of Open Content Educational materials.
- Open Gaming Center - an open content experiment to create a games and gaming encyclopedia
- Openlaw  - Experiment in the open crafting of legal arguments
- Open-Songs - Free, Royalty Free MP3's
- Opsound  - Open sound pool, a record label.
- Open Directory Project  - web directory like Yahoo.
- Open Music Registry  - Open sharing of music using an Open Audio License
- Open Photo  - stock photos
- OYEZ  - US Supreme Court multimedia
- Pickings.de (daily news review)
- Prelinger Archives  - government and advertising films
- Project Gutenberg 
- Public Library of Science 
- PlanetMath  - Math for the people, by the people.
- Wikimedia 
- Wikitravel  - travel guide (not part of Wikimedia)
- Woochi - Wine Encyclopaedia
- World66  - An open content travel guide (previously known as CapitanCook)
- World Lecture Hall  - Online course materials
- The Worldwide Lexicon