TinyMUD is the name of a MUD server codebase, and the first MUD running that codebase. The MUD itself has subsequently come to be known as "TinyMUD Classic" or simply "Classic", or occasionally "DaisyMUD" (since in the final days of its first incarnation, it ran on a computer named "daisy"). To distance itself from the combat oriented traditional MUDs it was said that the "D" in TinyMUD stood for Multi-User "Domain" or "Dimension", which led to the eventual adoption of the term MU* to refer to TinyMUD and its many derivatives.
Most modern MUSHes are descended from TinyMUD.
The TinyMUD server was originally written by James Aspnes in mid-to-late 1989 with the intention of focusing on player cooperation rather than point-gaining: it became the first so-called "social" MUD. TinyMUD was inspired by Skrenta's 1988 Monster. Aspnes announced the availability of the first TinyMUD on August 19, 1989; seven months later, on April 29, 1990, he announced TinyMUD's closure (due to the process size exceeding the memory limit of 32 megabytes on the host system).
TinyHELL was the second TinyMUD server and included a whisper command.
TinyMUD's database was briefly resurrected as "PlanckMUD" (named after the new machine it was running on, "planck") by Bruce Woodcock on October 8, 1990. Subsequently renamed "TinyMUD Classic", the goal of this project was to clean up and revive the database, as well as serve as a method of stress-testing the new server it was running on. The revival was very controversial among many TinyMUD players, but the new version was actually even more popular than the original. TinyMUD was shut down again on December 11, 1990 when permission to use the new server was revoked. This version of the TinyMUD database is believed to have been subsequently lost.
On August 20, 1990, the administrator of what was then the most popular TinyMUD, Islandia, took down that mud and put TinyMUD Classic up in its place for the day, calling it "Brigadoon Day", a reference to the musical Brigadoon, about a mythical village in Scotland that only appears for one day every 100 years. Since then, it has become a tradition to bring back old muds on August 19 or August 20 for the day. In particular, TinyMUD Classic has reappeared at this time almost every year from 1998 to the present at .