Google did acquired Jotspot long time ago for their wiki platform. Well, it took 16 months to relaunch it but it's finally out ! So go to sites.google.com to try them and in the case you have already a google apps account and you use the pages app, strangely enough, you have first to disable it, before being able to add the new sites app aka wikis !!

UPDATE: These wikis are here to integrate other google apps like documents and spreadsheets, but one thing that really sucks is that you cannot integrate a private spreadsheet. The spreadsheet has to be published on the whole internet ... I mean if I'm doing a private wiki, I want to share private spreadsheets !