The Longest Now

In tracking down groups to invite to Wikimania, I’ve discovered a
wealth of active wiki platforms populated by entirely different circles
of users, and promoted on different social/blog circles as well. Let’s
see how many I can list (NB: capitalizations not CaMel perfect):

• MediaWiki. Low on ACLs, manuals, and single-user snappiness, high on scalability and install speed. Server cluster compatible.
• Twiki. Oldie and goodie. Endlessly extended; a frankenstein of great bits that often work well together.
• Xwiki. Ludovic’s baby. Neatly modular, cleverly multilingual, a jack of all trades.
• Socialtext. The most open of the enterprise wikis. Pretty swell.
• JotSpot. The early leader in “how hot is enterprise wiki?” VC circles, afaik. Flashy.
• Confluence.
  Atlassian’s editable workspace; not called a wiki for the first year of
  its life. Compatible with an endless collection of databases and
  middleware platforms. Largest enterprise-wiki userbase.
• Snipsnap. Fundamental notion of snips, for transclusion and reuse.
• PurpleWiki. Niche case contender; primarily used by its creators and as an example application of Purple Numbers.
• UseMod wiki. MediaWiki’s ancestor. Stable. Unchanging. Stuck in 2001.
• Historical wikis : c2, meatball, others which helped mould the philosophy of the budding tool.
• Planned wikis Of The Future : WordPress-wiki (another
  contender for the name wikipress by another contender for the acronym
  WP?), WorldCat wiki, …

Free wiki hosts (with ads):

• In English:  wikispaces, with beautiful layout and inline stats,  wikicities (jwales & wikia), schtuff (brian), seedwiki (since 2001),  xwiki (ludo himself),  pbwiki …
• In other languages : [a few german hosts I need to look up.]

Other wiki hosts:

• Broken wiki hosts: atwiki, swiki (another xwiki site?), …
• Non-free wiki hosts :  Sometimes there is one combined with each non-free wiki platform… 

More entries, and links, to come… please suggest your own favorites
to add to the list. If you have favorite wiki hosts, free or non, you
can mention them as well. I’ll get around to doing a comparison of them
one of these days.