Google offers these services in a co-worker and student edition, but essentially the two services are the same.
You sign up with your school or office email and encourage your co-workers to do so. All of the people you want to collaborate with must have an email address from the same domain, and they must be signed up through Google Apps Team Edition.
You can specify who you want to collaborate on a specific document or site, or you can open the site up to anyone with the same domain. You can also publicly publish documents or keep them protected.
Google Apps Team Edition services include Google Sites, Google Docs, Google Calendar, Google Chat, and iGoogle.

