I use open writer for all my writing stuff.

Titanpad is also amazing for collaborating, and I was only notified of it's existence about a week ago. It's more or less shutting down in march, but pirate pad looks like it's the same thing. Basically it's a document that you and anyone with the unique url code can edit. It does not send alerts however. otherwise, it's very easy to copy and paste your finished collab anywhere, unlike skype.