The encyclopedia that preceded Wikipedia was Nupedia.
Nupedia went online on March 9, 2000, founded by Jimmy Wales and Larry Sanger and funded by Bomis. It aimed to create a free online encyclopedia, but its articles passed through a demanding seven-stage editorial and peer-review process before publication.
That careful system produced authoritative work slowly: Nupedia had only a small number of completed articles when Wikipedia began in January 2001 as a quicker, wiki-based companion project. Wikipedia’s open editing model attracted contributors at a dramatically faster pace, and it soon became the main project.
A common mix-up is treating GNUPedia as Wikipedia’s predecessor. Richard Stallman proposed GNUPedia as a separate free-encyclopedia effort, while Nupedia was the project that actually launched Wikipedia as a side project. Nupedia was discontinued in September 2003, and some of its content was absorbed into Wikipedia.