Available at http://office.live.com.
Basically, you need to use your sky drive as store.
I haven’t tried the integration with Office 2010, where you’re supposed to be able to share documents with other people and see them editing. I only have Office 2007 at work. With Office 2007, the file is locked altogether when you open it on your PC.
Now what we really need is an integration between Sky Drive & Live Mesh so that I can simply edit on one of my PC folder and have it being replicated to the cloud.
Pretty cool web apps nevertheless.