Zork, one of the first interactive fiction computer games from late 70s has been very popular during that period. Infocom is giving away, all three versions as free downloads for PC and MAC.
Zork I: The Great Underground Empire (1980)
Zork II: The Wizard of Frobozz (1981)
Zork III: The Dungeon Master (1982)
Get them here – http://www.infocom-if.org/downloads/downloads.html
How to get it working in Windows 7
Unzip the file and Launch _ZORK1.COM
This should open the MSDOS Window with Zork running
How to get it working in 64 bit OS
Download DosBox from http://www.dosbox.com/download.php?main=1 and install it.
Run it and type mount c: c:\ // Assuming you extracted zork to your c:\ drive
Now type c: // Change to the c: mounted path
Now type cd c:\path\to\zork
Now type zork1
You want to run the batch file — Zork1.bat/Zork2.bat/Zork3.bat