If you read Howard Rheingold's Virtual Community book, I know you will be at least semi-curious about MOOs. Following is some information about using MOOs, some MOO places to try out, and some links to sites which explain more about MOOs, how to use them, etc. Each room is associated with a textual description, and may contain one or more objects, each with their own textual descriptions.
MOOs provide a combination of tools.
A librarian in Connecticut sponsors online meetings with big-name people in librarianship and the internet. The Internet Public Library ran a pilot project where they accepted reference questions real-time from patrons from all over the country. For example, during a science experiment the students can use their online connection to ask the expert about the course of experiment MOOs are also widely used to foster reading and writing skills. Since students enjoy the process of chatting and leaving messages, they become more interested in communicating clearly and imaginatively. MOOs can be used to encourage role-playing in order to act out historical events.