Google Spreadsheet

"Google is today set to launch a Web-based spreadsheet program that will allow people to view and simultaneously edit data while conducting 'in-document' chat, a Google product manager said on Monday.

The launch of Google Spreadsheets puts the search engine in even more heated competition with Microsoft, whose desktop-based Excel spreadsheet program is a standard office tool. "

Limited test:
http://www.google.com/googlespreadsheets/try_out.html

Read more about it:
http://www.google.com/googlespreadsheets/tour1.html