Actually, I think rr supports shared memory operations under some circumstances... (I'd love to have my beliefs confirmed / corrected by somebody more knowledge

Actually, I think rr supports shared memory operations under some circumstances... (I'd love to have my beliefs confirmed / corrected by somebody more knowledgeable) My understanding is that rr has some handling for read-only shared memory and for arbitrary sharing within a tree of recorded processes. Undo's shared memory is different because it doesn't need the other process to be recorded, so you can do read/write sharing with arbitrary processes or devices. (disclaimer: current Undo engineer)