Google Docs & Spreadsheets

With Google Docs & Spreadsheets, you can:

• Use our online editor to format documents, spell-check and more.
• Upload Word documents, OpenOffice, RTF, HTML or text.
• Download documents to your desktop as Word, PDF and more.
• View your documents' revision history and roll back to any version.

This looks like a very interesting (and promising) service from Google. Check out Google's Tour.