The one program truly blew my mind at the time was Netrek - the first networked multi-player realtime graphical space fighting game. I've wasted so much time late into the nights playing the game in the lab instead of doing coursework.
The admin came to the lab from time to time and said we're hogging the workstations with the game and banned the game during daytime.
I remember ca. 2000 my best friend busting into my office, pushing me aside, logging in savagely to something and having a sight of relief.
He managed to send back a fleet or something - it was a real time game where you needed to do stuff at the right time (after sometimes a few hours). I do not remember the name of the game but it was fashionable for some time (not sure if it was text based or not)
Those games are still kicking around. Played Neptune's Pride a while back, would not recommend, seems designed to devour your waking (and what should be sleeping) life.
It's a fast paced multi-player space battle game with a top down graphic 2D view. It's like Command and Conquer, with each unit controlled by a different player.
The admin came to the lab from time to time and said we're hogging the workstations with the game and banned the game during daytime.