Evennia
Python MUD/MUX/MUSH/MU* development system
...Rather than prescribing a rigid game structure, Evennia gives you a bare-bones but powerful foundation: default systems handle networking, database/storage, server management, user accounts, characters, rooms, items, chat channels, and basic commands — but you define the gameplay rules, content, and game logic yourself in pure Python modules. Because you use regular Python, you get all the benefits of a modern language: familiar syntax, standard libraries, version control, and rapid iteration, rather than a custom scripting language. The framework supports both traditional MUD clients (telnet-style) and a built-in HTML5 webclient, making it accessible to users on browsers or standard clients alike.