What is the system model being simulated here?

I've played with it, and checked the source code, and this looks like a really, really simple control loop mechanism. It's basically P controller (as in, PID controller with I and D set to zero) and with this simple on/off "mode" selector wrapped around it that basically turns it off sometimes.

The performance seems _really_ bad: set manual input to -0.5 and watch it oscillate like crazy, with a very large amplitude. That mode selector is really not helping here!

The visualization is nice and very high-tech, but a well tuned PID controller would perform much better. Heck, even a simple P controller would likely perform better as well, at the expense of small steady-state oscillation.