Anyone familar with Google Spreadsheet? Apparently Google is in the testing stages of a spreadsheet program that will be web-based and free. They intend for it to compete with Excel, eventually, and one very interesting feature is you can have large groups of people all working on the same spreadsheet.
You can sign-up and try to get into their limited test:
http://www.google.com/googlespreadsheets/try_out.html
I signed up a few days ago, but have not heard anything yet. I think the first version is fairly primitive, but I see some interesting potential there.