Multi-User Shared Hallucination.
These are text-based role playing games, though different from typical text adventures (MUDs) in that the focus of these games isn't really about adventuring or killing monsters or each other. Instead, the focus tends to be depth of story, character motivations and development, and social interactions.
I used to play Atonement RPI a lot, though I don't anymore. I'm curious if any members of this community share an interest in these games, or know of any good ones to try?