I've posted about this on BGDF, so some of you may already have seen it, but I'm starting work on a project that would allow online prototyping and playtesting for tabletop games. I'm still early in process right now, but I've got a comparison of existing tools that you all might find useful.
This is a BRILLIANT idea and exactly what a site like this needs. I play test environment you can "feel" without having to print and cut cardboard. I could save so much time and headache with something like that. I'll check out the "similar products" you listed for sure. If you'd like to call out for help with yours, I'll do what I can.