Google Groups is Google's take on an aspect of the web that's been around for as long as the Internet--discussion boards. It is not fancy, but it can provide you with a great way to engage students in some informal writing and to engage them in discussion with each other about class concepts.
In the example above, AP English students have been asked to debate the issue of man's role in global warming. You might ask, why don't I just have them do this in a Google document? And the answer is that you could. However, it does open up some possible problems, especially when dealing with young folks who don't always make the best decisions. Since everyone who is sharing the document can edit it as they like, which could enable some ne'er-do-well to engage in electronic vandalism. Sure, you should be able to catch the culprit using revision history, but if someone were smart enough to lift another student's log in information, it might be hard to track down the true culprit.
Google Groups allows you as the instructor finer control over what is posted and even provides content filtering and the ability to flag for moderation posts that may be inappropriate . It can be somewhat complicated to set up, however, but once it's done, it can be a very effective tool for student writing.
Mostly, though, the students become very motivated by the opportunity to engage with and comment on each other's ideas. It can often result in very animated, but moderated, discussions.
