www.iforce2d.net

Maybe this feature exists in RUBE and I'm just not finding it because I don't know the terminology...

Is there a way to create reusable symbols or prototypes, so that I can build a scene, then update all instances of a given symbol at once by editing the "master"?

Not yet, but this is planned for a future update.

Awesome. RUBE is an excellent tool. I'm enjoying learning and using it so far. Much more stable and well thought out than other editors I've used... and written Thanks!