The UnOfficial Squaresoft MUD is free of charge, and can be accessed from almost any computer with an internet connection, as well as from a phone.
The absolute simplest way to play UOSSMUD is to click here to play right in your web browser.
If you want a better interface, you can download and install a MUD client and use that to connect to UOSSMUD. MUD clients are programs which connect to MUDs and usually offer additional helpful features, such as aliases, macros, triggers, and speedwalks. Some of the more popular MUD clients include MUSHclient and Cmud for Windows, as well as Mudlet, Rapscallion and Savitar for Mac. For Android, Andromud or MuClient is recommended. For iPhone, MUDMaster is a good choice.
If you connect using a client, you will need to know that the server for UOSSMUD is uossmud.sandwich.net, and the port is 9000.