Jotspot [ jot.com ], a wiki hosting provider. With extra (unique?) features like “e-mail to a wiki page”. Note: this is a for-fee service.
Lawrence Lessig uses Jotspot for a collaboration to update a new version of his Code and Other Laws of Cyberspace book.
Socialtext had that feature a year before they did, check it out.
oh. thx Ross! 😉Socialtext
Wikispaces did it, too !