Scratch

I  agree that it is a challenge, especially in an embedded environment with limited resources, and of course there will always be an upper limit on the projects that can be supported. In my experience though many projects do not have that many scripts running at once and I think, with careful design, Android can be made to support more scripts than one might expect.

How far did you get with this when you tried it before? Is your project anywhere online? And what limitations did you run up against ? I'd love to get your input on my project as someone who's been down that road before 

I do anticipate some potential performance issues with the graphical effects, but I think I may be able to mitigate them to some extent. I'm curious as to what problems you had with implemeting "touching" blocks though, as it's something I've yet to implement. Perhaps it will become clear when I do   

At the moment I'm using a fairly crude global lock to synchronize threads and emulate Scratch's thread semantics. This seem (so far) to keep the block timings predictable while also being reasonably performant, but obviously the overhead it adds would be unacceptable with a large number of Scripts.

I'm going to be doing some stress testing once I have some more features implemented, to see what's a reasonable maximum number of threads. Obviously the device is a consideration here, and I'm developing on a quad core phone. I'll need to get testing done on a variety of devices before I can make a decision on that...