Hmm, good question, concurrency and UIs seem a natural fit, what was some prior art and who used it first? I can name Modula-3's Trestle and Pike's Newsqueak l

Hmm, good question, concurrency and UIs seem a natural fit, what was some prior art and who used it first? I can name Modula-3's Trestle and Pike's Newsqueak language/GUI from the top of my head. Didn't Xerox' Mesa use threads for this?