It was based upon the MUD1 code by Richard Bartle and Roy Trubshaw, and ran until the machine that hosted it, a DEC-10, was superseded in 1991.
MIST was notable for its "dog eat dog" and "anything goes so long as some more powerful character doesn't decide otherwise" philosophy, so to speak. Wanton killing or tricking of other level users, or using magic powers to compel them to perform unexpected actions such as attacking others without warning — typically leaving them with the blame — was just as acceptable as supporting them, within the game world.