Google Docs offer a free collaborative word processor, spreadsheet, and presentation tool.

docs.google.com

Resources:

What are Google Docs?

http://www.commoncraft.com/video-googledocs

Classroom Ideas:

http://docs.google.com/View?docid=dcdn7mjg_72nh25vq

Google Docs Template:

http://docs.google.com/templates

Good to know:

+ Google Docs now allow anyone to view / edit without an account!

+ Google Forms feed directly into a Google Spreadsheet.