Optionally turn on turbo mode by shift-clicking the green flag, then let it run and watch as the "approx. pi" variable approaches pi!
I was sitting in a lecture when I suddenly remembered attempting (and failing) to make this when I was a kid, and it occurred to me how trivially easy it would be as a grown up. So, I threw this together in like 30 minutes. As an added bonus, the visual it creates is pretty mesmerizing. There may or may not be too much imprecision in there for it to ever get more than a few digits, but whatever man. Background music is The Flower Called Nowhere by Stereolab