I had seen WIMP (windows icons menus pointers) interfaces before I saw a Mac. BBC Micro I think. No mouse, but keyboard could achieve the same thing. Ok, that was for specific applications, and not the OS that was based on it though.
Yep, they sure existed (for example at Xerox Parc as well), but Macintosh was the first mass marketed one. To be fair, I guess mass marketed is a subjective term :)