(This is a plug, but some members of this list might be interested.)
I have just released YP Waves 1.0, a new Macintosh program about waves.
This program can be used to teach waves characteristics (amplitude,
wavelength, etc.), the superposition principle, standing waves,
interference of waves, beats, etc.
According to Macdownload.com (ZD Net): "YP Waves is a new release from
Yves Pelletier, the master of the educational science application. (...) If
you're a science teacher, student, or just like to play with cool science
applications, check out YP Waves. Rating: 4 mice."
Also available from my web site: YP Projectiles, YP Refraction, YP
Reflection, YP Electric Field, YP Slider Crank, YP Magnetic Force, YP Gear,
YP Planetary Gear, YP Image, YP Vernier, YP Vectors, YP Collisions, YP
Circular and YP Shadow. All of them require a Macintosh computer.