App: Ripple Tank
Developer: Falstad.com
Genres: Education

A simulation of a ripple tank, or wave tank. Make waves with your finger, or view examples including such wave phenomena as interference, diffraction (single slit, double slit, etc.), refraction, resonance, and the Doppler effect.

Create your own experiment and save it for future reference.  Create objects (boxes, ellipses, walls, media) and move them around.  You can also record videos.

Release notes:
update for Yosemite