Need a link to a game, but I don't know what it is.

I’ve been reading up on those old… What do you call ‘em, video games. You know, the really old ones. Where you would type in the command and the character would follow it? I’m not sure what the genre is called, or of any specific games in it. But, If you know what I’m talking about, can you tell me where I can access a free one online or download one for free? Preferably it would work on a mac, but windows would work too. Thanks!