MUF (short for Multi-User Forth) is a Forth-based programming language used on TinyMUCK MUCK servers and their descendants, including Fuzzball MUCK, ProtoMUCK and GlowMUCK.MUF is the system programming language for TinyMUCK systems. Many fundamental MUCK commands, in fact, are implemented as MUF programs, and built-in commands of the MUCK server are often replaced with more sophisticated versions written in MUF.