Apple's Macintosh did this in 1984. Files were tagged with 32 bit codes: one for the "creator" (the associated app) and one for the type. These were often made up out of readable characters: a so called "fourcc" (four character code). The "fourcc" persists in cross-platform media formats.
The first software I ever sold online was an app that would change the creator code of a file to whatever application you wanted. For some reason, there was no obvious built-in way to do that in Mac OS 8 (besides opening the document in the other application and saving it, or changing it in ResEdit).
I only ever sold one license, but I was 12, so I was pretty excited.
