Colossal Cave - The first adventure game - still fun all these years later.

I know, not exactly new, but could be a new experience for many younger users. I remember playing this at the end of my last year in secondary school on the school's Cromemco Z2D ( http://microship.com/cromemco-z-... ) in 1980. Since then, I've probably played it on every platform that I've used, right up to iOS. Not many games have lasted that long and remained playable on so many platforms.