MediaMOO
A text world at the MIT Media Lab where you didn't play, you attended a conference — a virtual meeting place for media researchers, opened in 1993.
Amy Bruckman, a Media Lab graduate student, built MediaMOO on the same server code as LambdaMOO and opened it in January 1993. The difference was who got in. Anyone wanting a character had to submit an application describing their research, and the world was laid out as an academic setting with seminar rooms, offices and regular gatherings instead of caves and trolls.
The point was to show that a MOO could work as a professional network, and it did: researchers who had never met traded ideas across continents in real time years before video conferencing was something you had on your desk. Bruckman built on the experience with MOOSE Crossing, a MOO where children learned to program.