You can play the Atomistic Simulation Game (or applet) that I recently made using Unity 3D. It is an atomistic simulation, that utilizes Lennard-Jones potentials. I simplified some aspects, so that it can be run like a game in real time. It is still pretty realistic for educational purposes. You can click and drag an atom, or you can increase or decrease the temperature. The interaction between the atoms is limited to some variable length, so distant atoms may not attract each other, to save computing power.
I did not have the time to apply something like a periodic boundary, so they can drift around. The units, and parameters are arbitrary.
I wrote an atomistic simulation, some years ago when I was conducting my masters study, while we were taking the atomistic simulation course from Prof. Dr. Kadri Aydınol. That time it took a very long time using FORTRAN. Recently, while dealing with some projects using Unity 3D, I was thinking of making an atomistic simulation, but thought it may take lots of effort. Later I realized it will be very easy thanks to Unity 3D. And I made this in a incredibly short time.
You are free to use it for educational purposes.