- 1902 Encyclopedia
- Articles and illustrations from the Encyclopaedia Britannica, 9th Edition (1875) and 10th Edition (1902). Searchable by keyword and browsable by subject index.
- Again, But Slower
- Displays Wikipedia articles and their simpler counterparts side by side.
- EncycloMedia
- Free online encyclopedia for all ages. Explore a vast library of multimedia articles and information on a wide range of topics. Learn interactively with online videos, pictures, and more.
- Encyclopedia Britannica
- Provider of learning knowledge products through its online resources and distributed books and products.
- Encyclopedia Smithsonian
- Offers images, video and sound files from dozens of Smithsonian libraries, archives, and museums.
- Information Please
- Knowledge resources featuring almanacs, atlases, encyclopedia, discitonary, thesaurus, and white pages.
- Wikia
- Offers a large assortment of topical wikis, as well as the traditional ability to edit them.
- Wikipedia
- Free open-source multilingual encyclopedia.
- World Book, Inc.
- Official site promoting its excellence in the production of award-winning encyclopedias, reference sources, and multimedia projects for the home and schools.
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