Math, physics, and engineering java applets

Some educational java applets to help visualize various concepts in math, physics, and engineering.

http://www.falstad.com/mathphysics.html
http://mathdl.maa.org/images/upload_library/4/vol4/kaskosz/derapp.html
http://www.wolframalpha.com/
http://cs.jsu.edu/~leathrum/Mathlets/

Here is a example of a circuit simulator (with pulse generator circuit):

http://www.falstad.com/circuit/