There *is* a superficial functional resemblance to Macromedia Contribute, but a closer look shows that these are very different types of workflows:

Adobe Co-Author: A site designer can specify special editable areas in an HTML document. A content contributor can then edit each of these areas, one at a time, in a form-based application.

Macromedia Contribute: A content contributor can browse to an HTML page and then (assuming they have site privileges) can edit that content while looking at the whole page. Optionally, a Dreamweaver (or GoLive!) designer can use Dreamweaver templates to lock out areas from editing.

Differences:
– With Contribute you default to full editability, with protected regions as an option… with Co-Author you default to no editability, with editable regions as an option.
– With Contribute you write while looking at the page… with Co-Author you can call up an editable area in another app, rewrite, publish, and then look at the new page in a browser.

Recent versions of Macromedia Contribute also do a lot more with permissions, connections, versioning, notifications, rollbacks… aside from the basic editing features there’s a ton more in Contribute.

If you’re still not convinced, try searching the main GoLive list with term “Co-Author” in message body… seems most Adobe GoLive users recommend Macromedia Contribute to each other, even though they have a free Co-Author license included with each GoLive purchase.
http://listsearch.com/GoLiveTalk.lasso

Regards,
John Dowdell
Macromedia Support