Which web-based encyclopedia was the predecessor of Wikipedia?

Nupedia was an English-language web-based encyclopedia whose articles were written by volunteer contributors with appropriate subject matter expertise, reviewed by expert editors before publication, and licensed as free content. It was founded by Jimmy Wales and underwritten by Bomis, with Larry Sanger as editor-in-chief. Nupedia lasted from October 1999 until September 2003. It is mostly known now as the predecessor of Wikipedia, but Nupedia had a seven-step approval process to control content of articles before being posted, rather than live wiki-based updating.

Nupedia was designed by committee, with experts to predefine the rules, and it approved only 21 articles in its first year, compared to Wikipedia posting 200 articles in the first month, and 18,000 in the first year. Unlike Wikipedia, Nupedia was not a wiki; it was instead characterized by an extensive peer-review process, designed to make its articles of a quality comparable to that of professional encyclopedias.

Nupedia wanted scholars to volunteer content. Before it ceased operating, Nupedia produced 25 approved articles that had completed its review process (three articles also existed in two versions of different lengths), and 150 more articles were in progress. Jimmy Wales preferred Wikipedia's easier posting of articles, while Larry Sanger preferred the peer-reviewed approach used by Nupedia and later founded Citizendium in 2006 as an expert reviewed alternative to Wikipedia.