See the full post for details (or this Office Web Apps blog post)– limited features at this point (e.g., you can create new PowerPoint and Excel files but not Word or OneNote files/notebooks; you can view Word files) but still very interesting
Microsoft Office Web Apps is a free online version of Microsoft Office that includes Word, Excel, PowerPoint, and the OneNote Web App.
Using Office Web Apps, you can view as well as edit Office documents on any computer and since these apps work inside the browser, you can even edit Office files on a Mac without requiring the Office software.
Sign-up for Office Web Apps
If you are not signed-up with Office Web Apps yet, here’s another opportunity: