TinyHELL is an early Multi-User Dungeon and the second TinyMUD

TinyMUD

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"...

 server, and has been noted as a well-known TinyMUD of its era.

Summary

Some of its features were "Limbo" (a room described as an "endless mist" which characters started at), the Hellgate Pocket Dimensions Nexus, which lead players to various locations, some which had Nexi of their own, and the Crystal Palace, a very large Hotel for people to build from.

TinyHELL was put online in December, 1989 using the TinyMUD

TinyMUD

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"...

 code just after its initial release by the author. Run by two student employees at the University of Oklahoma

University of Oklahoma

The University of Oklahoma is a coeducational public research university located in Norman, Oklahoma. Founded in 1890, it existed in Oklahoma Territory near Indian Territory for 17 years before the two became the state of Oklahoma. the university had 29,931 students enrolled, most located at its...

 Engineering Computer Network, it lasted for several months before being replaced by successive MUD servers.

TinyHELL was the originating point for several modifications to the TinyMUD

TinyMUD

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"...

code base, including the first addition of the whisper command and the HAVEN and ABODE flags.