MOOs work on the idea of a virtual, text-based world.
With a MOO, you telnet to a host and land in a virtual room, and you can converse with anyone else who has connected to the same host and who shares that room with you. You can also move from room to room, and you can page people who are in other rooms. A MOO also allows the creation of virtual objects to assist instruction. The virtual video recorder allows you to have an actual record of the discussion. There are virtual blackboards as well, on which you can post discussion questions.