Wikidot's population is 4.

Wikidot was created on 2006-08-01.

There are many places you can get a free private wiki. One place is WikiDot. The perk with this website is only people with certain log in information is able to view the wiki info.

Google Sites is pretty simple and certainly neat and ad-free, but it's fairly limiting.

There's always Angelfire, but I haven't ever tried that.

Freeweb's probably still floating around somewhere.

If you want to make a wiki-style site or even use the wiki format to your advantage, I highly recommend Wikidot. It's relatively simple to use and they've got tutorials for almost everything.