I treat it more like a blog, but it is a wiki, as the author takes pains to remind people. Alex maintains a wiki engine of his own, and is an enthusiastic advocate of the medium.
One of the oldest wikis still around, along with the original. It helped rekindle my interest in the medium earlier this summer, but it's not very inviting, even though the subject matter should be very relevant to me.
An even older wiki, with a similar focus to CommunityWiki, except broader. Much less active, too, but with more information on a variety of topics (not least because other wikis defer to it).
Another old wiki, ostensibly about the Tcl programming language and related topics, but with many interesting nooks and crannies. Fairly active as of 2021.