There's a program for Mac OS X called "Cantrip," which can befound at versiontracker.com. It allows you to connect to these different servers where you can play addicting text-based RPG games (your Terminal program can do this too with the "telnet" prompt). Just a couple weeks ago, my friend told me about "mudding" and I tried it and got hooked. If you want to try out a MUD server, try the follwing addressees:
Address - lots.wolfpaw.net
Port - 3000
Game - Legacy of the Sith (a Star Wars game)
Address - mud.labyrinth.net.au
Port - 3333
Game - DominiaMud (based on Magic: The Gathering)
Once you MUD for a while, you will get used to the commands you need to type. Experienced players who have played for a while already can help you out if you talk to them. To get you started, I'll give you some basic commands that can help you get around.
To move south - s
To move north - n
To move east - e
To move west - w
To attack somebody - kill 'target'
To flee - flee
To pick something up - get 'item'
To talk to somebody (in the first few levels to get help) - newbie 'message'
I'm sorry for posting this, because you should be aware that hours and hours will be spent "mudding" if you are addicted. I'm warning you.