There are many resources available on the net that are in the public domain, and therefore freely usable without restrictions for Wikipedia content. There are also many copyrighted resources whose licensing terms are liberal enough that they can generally be used as well. Below is a list of some of each; please add to this if you discover new resources.
True Public Domain Resources
These resources are completely free of copyright restrictions, and can therefore be used and modified at will for any Wikipedia page. Some (such as Project Gutenberg texts and the public domain dictionary) are in the public domain either because the author has renounced their copyright or because they are very old and their copyrights have expired. (Care should be taken to bring such texts up to date.)
Keep in mind Wikipedia is not a dictionary, though entries should begin with a good definition.
- Project Gutenberg See in particular The Project Gutenberg Encyclopedia (although only Vol 1 of this seems to be available). Note that not all of the Project Gutenberg text are fully in the public domain. Read the license of the respective texts carefully.
- Bulfinch's mythology from project gutenberg
- Online Book Initiative
- Images of American Political History
- The Household Cyclopedia
- U.S. Census Bureau Has an enormous range of facts and figures which we will find helpful in fleshing out articles about cities and states.
- Occupational Outlook Handbook Contains descriptions of a great many occupations such as Physical Therapist.
- GIMP Archive Royalty-free photos
- CIA World Factbook Contains basic facts on all the countries of the world.
- U.S. State Dept.: Background notes on the countries of the world. Also see their copyright notice, which, as you'll see, places material that is not explicitly copyrighted in the public domain.
- The Jargon File Eric S. Raymond's definitive work on geek-speak.
- Perry-Castaneda Library Map Collection, Univ. of Texas Contains maps from all over the world.
- Perry-Castaneda Library Portrait Gallery, Univ. of Texas Contains portraits of famous historical people.
- Physics for Free has two public domain physics books by a Yale professor: one about basic physics, one about groups and particles.
- Public domain lecture notes: "Introduction to Computer Science", "Data Structures" and "Analysis of Algorithms"
- Hypertext Webster Gateway A searchable interface to a 1913 public-domain Webster's dictionary, downloadable here: Public Domain Dictionary
- Biblical dictionaries: Some late nineteenth century Biblical dictionaries; these might need work to render unbiased and up to date.
- NIST Dictionary of Algorithms, Data Structures, and Problems: Huge, high-quality resource. All entries are in the public domain except for a few that carry an explicit copyright notice.
- Christian Classics Ethereal Library: A project similar to Project Gutenberg, but focusing on Christian texts.
- The Online Books Page: A comprehensive index of books available on the Internet. Most are public domain, but not all; check for copyright restrictions.
- Public Book Shelf
- NOAA Photo Library: The American National Oceanic and Atmospheric Administration has put its massive photo library in the public domain. They ask that NOAA is given credit for the photos. The collections are simply amazing.
- Federal Emergency Management Agency: Not sure how much of this is useful, but anyway it's under the same terms as the U.S. Department of State site: all in the public domain unless it carries an explicit copyright notice.
- U.S. Environmental Protection Agency: copyright notice here, typical U.S. gov't terms. Does have some good information for people patient enough to find it. :-)
- U.S. National Toxicology Program: copyright notice here, typical U.S. govt terms.
- U.S. Navy, Info on specific ships
- Air Force Link
- Medline at the NIH copyright terms here indicating materials in public domain unless indicated otherwise
- UNSECO Public Domain Resources and Virtual Library at this URI
- Images of American political history: At this URL PD images, mostly monochrome.
- Yellowstone National Park PD images
- PD photos of famous psychologists
- Scanned and colorised etchings claimed to be PD images
- NASA photos
- U.S. Fish and Wildlife Service pictures
- Public domain works done for NASA by Don Davis: high-resolution scans of space-related paintings.
Other "Free" Resources
These resources are copyrighted and licensed under terms that allow free redistribution in some form. There may be requirements to credit the original authors, or restrictions on making modifications. Check the license posted on each site for such restrictions.
- Nupedia.com: Read about adding Nupedia articles to Wikipedia.
- The Anarchist FAQ: Under GNU Free Documentation License. Contains much information on anarchism, but be careful, because a lot of it is biased towards a particular viewpoint.
- Free Online Dictionary of Computing was originally published under a license which required acknowledgements and was therefore not compatible with GFDL. Has recently been relicensed under GFDL and can be used by us. See Free On-line Dictionary of Computing/Status to help with importing articles.
- Planet Math: A collaborately developed math encyclopedia, under GNU Free Documentation License.
- Trinity Atomic Web Site
- ibiblio.org is a major repository of information, some of which is open content, and has a lot of links to open content resources. (If someone would like to search through the website to find and link to the stuff Wikipedia might potentially use, that would be great.)
- Connected: An Internet Encyclopedia was last updated in 1997. Here is their license: "Copying and redistribution of Connected: An Internet Encyclopedia is freely permitted, as is the creation, copying, and distribution of derivative works. The Requests For Comments (RFCs) are covered by a separate copyright, included below." I think we should contact the editor before importing anything into Wikipedia.
- The UK Public Records Office publishes documents that are Crown Copyright This allows "accurate" reproduction with an acknowledgement.
- Pubmed Bookshelf: Well-known biomedical books (eg "Molecular Cell Biology" and "Modern Genetic Analysis") put on the internet by the US government as an associated resource with the Human Genome Project.