Pythagorean Dissection
Saw a version of this as a gif on Tumblr,
http://curiosamathematica.tumblr.com/post/61569644908/twoblueeinsteins-animated-proof-of-the,
and had to dynamicize it.
Now we can see it works for any two squares, which means any right triangle. Right?
More GeoGebra at mathhombre.blogspot.org