I am not sure if there were any other implementations of overlapping windows on the Alto other than Smalltalk-76 (which was what Steve Jobs saw in his famous visit to PARC). The windows idea was cleaned up and implemented in more static languages for the Star, of course.

As Dan Ingalls mentions in his recent HOPL (History Of Programming Languages) paper, several times an idea would be discussed between different groups and in the next meeting the Smalltalk guys would show it working while the other groups were still sketching on the whiteboard. Seeing the idea in action would prompt them to also implement it in Mesa or similar language.