There was a dude who came to our school in Melbourne Australia from the United States, I would have been 13 so that makes it 1988. We had C64s and this American dude loaded GEOS onto one and started using it for a bit of stuff. We were flabbergasted as we didn't think the C64 was capable more than just Logo or a few games, I think we might have had some terrible CBM wordprocessor but GEOS kicked the pants off it. Sadly by this time we were getting PC based and there was also a Mac 512k in head teacher's office that you could use with permission. So it was not more than a novelty but I still think that GEOS is an amazing bit of kit.
cheers Nick