I saw via Memeorandum and Steve Rubel that Writeboard was about to launch, and lo and behold, the new collaborative document editor / word processor from the 37signals folk is up and running. It's going to get mercilessly compared to Writely (which I've been using for a bit now and can safely say is the cat's meow), but there are some major differences.

Writeboard is very single document based — you can create multiple Writeboards, but there is no "dashboard"-type interface where you can see them all the only way to manage them all is via Backpack. If you don't use Backpack, the best you can do is get a list sent to your email address of all the Writeboards you've started (which assumes you've used the same email address…). Conversely, Writely is great for keeping a working collection of documents and organizing them via tags. Both Writeboard and Writely have ways to send your document elsewhere: Writeboard can email your doc or save it as text, while Writely can export to a Word doc or a Zip file (you can also view the HTML source of the doc); both offer RSS feeds of changes.

Both allow you to invite collaborators in to work on your documents via email. Both have decent revision control so you can compare versions of the document and see which changes were made by whom. Both are chock full of AJAXian goodness, with clear and easy to use interfaces. In the end, I find Writely more appealing for its ability to manage multiple documents easily in a single interface. It can just as easily be used to store your collection of private, non-collaborative documents in one centrally-located, web-accessible spot — regardless of whether or not you take advantage of the collaborative aspect. If you need to collaborate on more than one document at a time, Writely also has a clear advantage. But if your group already uses other 37signals products and is familiar with their document syntax, or if you already use Backpack, Writeboard is of similar quality and ease of use as Basecamp, Backpack, and Tadalist, and won’t disappoint.