Zork

Zork was the second of the IF games to appear, based upon Adventure by some MIT college students. They went on to form Infocom (a now defunct company purchased by Activision) and released over 30 different text based games. Zork is one of the predecessors to MUD, which in turn lead to Diku, Merc, Rom… Ansalon. Thank you to all of those who paved the way. – Zivilyn.
Zork

Zork 
ZORK I: The Great Underground empire
Copyright (c) 1981, 1982, 1983 Infocom, Inc. All rights reserved.
ZORK is a registered trademark of Infocom, Inc.
Revision 88 / Serial number 840726

West of House
You are standing in an open field west of a white house, with a boarded front door.
There is a small mailbox here.

>open mailbox
Opening the mailbox reveals a leaflet.

>read leaflet
(taken)
"WELCOME TO ZORK!

ZORK is a game of adventure, danger, and low cunning. In it you will explore
some of the most amazing territory ever seen by mortals. No computer should
be without one!"