MU Index is a directory for the MU hobby, covering MUSHes, MUDs, MUCKs and MOOs. It helps visitors discover and explore games by name, theme, codebase or host, with options to browse the directory, find a random game, and consult an archive, learning materials, references, ecosystem information and rankings. The site also lets users submit games and offers sign-in and Discord access.

A central feature is its attention to the source and age of each listing detail. Facts are identified as either measured by the site’s crawler or declared by the game, allowing visitors to understand how information was obtained. The directory tracks game availability and population, distinguishing populated listings from those with unknown population, and reports crawler activity, including recent probes and newly discovered games. Visitors can also view trending titles and see when games were last noted or checked. With a multilingual interface, including English, Chinese, Japanese, German and Dutch, MU Index serves as a discovery and reference resource for people interested in the diverse online MU gaming community.