Does what it says: creates an online chat room. Think MSN, Skype text chat, etc.
Probably more suited to our uses, as it's less "instantaneous."
The forum is an online discussion board sort of deal, where learners can respond to comment threads and post new topics.
You can leave it completely open, or provide initial starting topics to get learners talking.
There is a "combined" or "split-screen" activity that combines a share resources activity with a forum, so learners can post links and documents and then comment on them in the forum.
The scribe activity is unique in that it is the only LAMS activity to select one 'key' learner from the group.
This learner acts as the 'scribe' and collates a report that all other group members must agree on before it can be submitted.
In that sense, it doesn't work well on it's own, so we pair it with a chat or forum to keep learners talking.