Detexify LaTeX handwritten symbol recognition
detexify.kirelabs.org
detexify.kirelabs.org
I find that for common symbols, it works _beautifully_. But for symbols that can be drawn in different ways (consider \cupdot for example), it seems to bork and return unrelated symbols.
One thing that I would find quite interesting is someone writing something similar that, instead of using gesture recognition uses image comparison. I realize it would be quite difficult, slow, and probably would have terrible accuracy, but meh . . . I should try that.