I have used Google Drive/docs quite a bit. I like that I can share and edit and collaborate with those within and outside my organisation so easily! Google Docs is also a great tool to share with students- as so many of them do group projects.
I have used Google Docs to collaborate about workshops, and also about Twitter ‘Secret Santa’ and ‘Secret stork’ events. Secret santa is a bunch of twitter tweeps who send a secret santa to another person at Christmas. I coordinate the names/details/addresses with a couple of other elves! The same works for our ‘secret stork’ spreadsheet as there are a number of Twitter friends who are expecting babies!
I have also used DropBox.
I have also used wikis, but not as much any more. Of course I use Wikipedia all the time, but find wikis have to be updated otherwise they lose their use. We do use an internal SharePoint wiki at work for procedures and that seems to work well.