Wiki existed for years before Wikipedia was started, and they have a nice article about it. I encountered wiki a couple of years before the turn of the millennium and it blew my mind, one of several formative experiences toward better understandings of the web, hypertext, and perhaps most of all collaboration and community, in general and of course in particular on the Internet.
This website you're looking at right now is a wiki of sorts, using a particular software project called Wagn.
Wiki is blogging's older, slower, less linear, more influential step-cousin.
The original wiki - the Portland Pattern Repository, also known as Ward's Wiki, was built to support the development ofa pattern languages of programming and succeeded at least in developing a set of patterns for programming, and sparking mass interest in that way of approaching programming.
Personal public wikis of note: