interesting.
i have not encounter this before until today.
http://demonstrations.wolfram.com/ChargedParticleInUniformElectricAndMagneticFields/ [img]http://demonstrations.wolfram.com/ChargedParticleInUniformElectricAndMagneticFields/HTMLImages/index.en/popup_6.jpg[/img]
think the commercial software also has the same idea of open source.
the simulations are not bad, the codes seems to be mathematical based as well.

downloading the player now to check it out.

guess the main difference is teacher can make free sims on easy java simulation to benefit humankind, improve learning in classroom, improve own pedagogical understanding, professional develop and learn.