Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its 16 million articles (over 3.4 million in English) have been written collaboratively by volunteers around the world, and almost all of its articles can be edited by anyone with access to the site. Wikipedia was launched in 2001 and is currently the largest and most popular general reference work on the Internet.
The name Wikipedia is a portmanteau from wiki (a tec... Registration not required.
Encyclopedia.com provides you reference entries from credible, published sources like Oxford University Press and Columbia Encyclopedia.
At Encyclopedia.com, you get free access to nearly 200,000 reference entries from sources you can cite. Plus, more than 50,000 topic summaries feature related pictures, videos, topic summaries, and newspaper and magazine articles from around the world. Encyclopedia.com also provides innovative tools that allow you to rate and sort the reference content you find... Registration not required.
MEDgle is the first health information engine of its kind: a powerful computable database of a body of medical knowledge so huge and complex, no human mind can hold and process it independently. MEDgle collapses billions of medical possibilities into comprehensible probabilistic clinical information, in real-time. MEDgle's content has been built and reviewed by physicians, every step of the way. Registration not required.