MUD

MUD is short for Multi User Dungeon, or in other words, MUDs are what MMORPGs were before they became complete shit. Many MUDs are still available, though to really enjoy them, you would require a MUD client.

While it's possible to play a MUD with no client software and just using telnet, MUD clients like tintin++ allow you to make aliases for common commands, set up triggers so that various mundane tasks are taken care of automatically, and can even allow you to map out the area as you play.

The simplest way to play would be to open a command shell and type telnet dragonswordsmud.com 1234 (as an example) and then after giving a name you would be asked to start a new character and then you could choose a race, and a class.

The game is all text, with the only "graphics" being whatever ASCII drawing the area builder threw in there and some colored text. The only thing you have to tell you what's happening is the room description. Since this means you have to do a whole lot of reading, you probably will give up before you get started.

tl;dr: You'll get bored before you even start.