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To the OP: If you are referring to Interactvie Fiction games like Adventure/Colossal Cave or Zork you can have then download Frotz for PC or Zoom for Mac and then download files from HERE to play on those emulators.

Some good games are of course Zork, Adventure, which are the originals, but also newer games like Photopia and LostPig are good for getting people started out in Interactive Fiction

Also, for people with iphones/touch and ipad, there is a free app called Frotz that games preloaded with a bunch of IF games.

edit: If they really get into Interactive Fiction have them look into Inform7, which is a language specially designed for making IF games. I did a project in it last year.
 
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