This is cool, but it has some serious numerical issues that ought to be ironed out. I took their example cubic function, and plotted the first, second and third derivatives. The third derivative goes crazy as x goes away from zero. (See screenshot http://farm6.static.flickr.com/5088/5361267299_a976c64dcb.jp...)

What does LGPL even mean in the context of a client side tool... it's not like you have any sort of linking in the C-sense of the term.

It really depends on how you use it.

Slick. Could use a way to generate a URL for an equation.

EDIT: There is, but it doesn't seem to work e.g.

http://graph.tk/#y%3Dsqrt(1-x%5E100)

http://graph.tk/#y=sqrt(1-x^100)

This is a great idea - any plans for 3d plots?

This is so cool, just in time for me working on a popularity ranking algorithm.