Selected from Chemsoft's Gas Simulation:

GasSim package. The 2D-gas simulator can generate many properties of an ideal gas like pressure to volume, pressure to temperature relations, Carnot cycles, diffusion, random walk, speed distribution, velocity distribution, barometric law in a gravitational field, and more. The only physics entering the algorithms are Newton's three laws. An extensive tutorial and many demonstrations accompany the set.

In Sept. 2009 we have (finally) coded simulated in addition to theoretical volume changes, isothermal and adiabatic. Although these features are still rather slow it is now possible to follow the generation of isothermal and adiabatic pressure-volume changes without any prior assumptions about a functional relation. It comes as no surprise that the Gassim model verifies the well established gas laws.
Gassim and the other Pascal programs now run smoothly in DOSbox (Windows, Linux, and Mac).