Google Spreadsheet, which will be made available on a limited test basis, follows Google's March purchase of a company offering a Web-based word processor called Writely.
The two Google Web-based applications represent possible challenges to Microsoft Corp.'s core personal-computer software business. Microsoft's Word and Excel dominate the word processing and spreadsheet markets." (from Wall Street Journal via Battelle).
It seems that a link to the Google Spreadsheet application will be available in the morning at Google Labs.
"Google's spreadsheet isn't as sophisticated as Excel. For instance, the Google spreadsheet won't create charts or provide a menu of controls that can be summoned by clicking on a computer mouse's right-hand button.
The program's main goal is to make it easier for family, friends or co-workers to gain access to the same spreadsheet from different computers at different times, enabling a group of authorized users to add and edit data without having to e-mail attachments back and forth." (from AP)
For the moment, good online spreadsheet applications are NumSum and iRows (you can see a screenshot for iRows below; the site is down - maybe Google has just bought iRows? But why Google Spreadsheet doesn't include charts then?).
More: Join the limited beta.