OpenEuphoria

https://www.youtube.com/watch?v=72y2EC5fkcE

Where would you even start? One small point: "No multithreaded support so far", which is probably quite wise.

At least I'm not completely alone: https://www.youtube.com/watch?v=D2AW9PMSHTw - and I have to wholeheartedly agree with the comment made at 19:00

One thing I would put good money on is the gui side being oft-redrawn from some internal state, rather than reverse execution somehow "undrawing" things.

Another take on "time travel debugging" (no sound): https://www.youtube.com/watch?v=_bbxR503-u0 and perhaps https://www.youtube.com/watch?v=MJCYQzeL-w8 which give a subtle hint what all those logs are, and how wrong I was to completely ignore them in the first video, and is slightly strange in that the critical functionality seems to be half in the editor and half in the app being developed...

I think the first step (intellectually speaking) is to divorce the debugger from the runtime, make them two communicating processes. Then (again, more of a thought experiment than recommended reality) you could introduce a middleman that convinces the debugger to display any whacky stuff, independent of what has/will/did happen. Add in some queries of logs of what happened when, and you're getting there...

PS: I love my 19:00 link. (it would o/c be much slicker without all the adverts)

PPS: I guess this forum really is finally completely dead.