A big part of the design work was trying to get it to be good at that, while still being entirely tree based. But you'll have to judge yourself how successful I was.

Well, your judging that would be easier if you could use it, rather than just read about it... I still have the source code, but since it was designed to work with a vector graphics display attached to a PDP-11, getting it to work in a modern environment would take some work. We had only one vector graphics display, so there was no chance then to have a significant user community, which was another problem.