What is the simplest, quickest, least obtrusive wiki site out there?

I’ve seen Mashable’s top 100 list, or even the three listed in common craft’s wiki video, but all these wikis require all collaborators create accounts (google docs counts here), give lots of editing options, provide a discussion board, posting of images, etc.

Is there a wiki site out there where one creates basically a subdomain that is a blank slate that can be edited and saved by anyone that knows the url (or perhaps a url and password). It’s fine if the creator has to make an account, but as long as it’s easy for everyone else, and it’s simple, it’s good even if the wikis self delete after a period of no use. Maybe such a thing doesn’t exist…