Google has launched a service called “Google Docs and Spreadsheets” (they have kept away from “Google Office” for some reason. Maybe we will see this when new services are added). It’s not really new but is a merger of Writely and Google Spreadsheets.
It places a lot of emphasis on collaboration and you can share your documents and spreadsheets and allow other people to edit them. Each file is given a unique URL that you can send to firends and colleagues. People who you invite to collaborate can also invite other people to collaborateand you can alter this on a file-by-file basis.
The interface is consistent between both applications for people who had problems with Writely. I also like the feature where you can send an email which is then converted into a document. I don’t know whether this was already a feature with Writely but I really like it.