Citizendium was founded in 2006 by Larry Sanger, co-founder of Wikipedia (and Nupedia). A big reason he created Citizendium was because of the failure of the old Nupedia. He left Citizendium a few years ago.
Citizendium was meant to be higher quality than Wikipedia, and meant to express the viewpoint of experts. On Citizendium, you can't just get a username and password and start editing; you need your real name, email, and a brief essay about yourself. This gets submitted to the Citizendium constabulary, who contact you, so you can be verified as being who you say you are, as well as being a verified expert. It is then that a user can edit. There are more powerful users (who are actually given the title "editors"), who have to be verified, and they approve and disapprove articles (in addition to modifying them). Even though there are several thousand articles in the Citizendium, only about 140 have been verified and approved as high quality.