Ising is a simple model of magnetism. It simulates a ferromagnet using a two-dimensional array of interacting spins at fixed temperature and magnetic field. The Ising applet was developed as part of the STP project. Additional examples of its use can be found on that site.
The goal of the STP project is to promote innovation in all aspects of the teaching of statistical and thermal physics in the undergraduate curriculum, including laboratory experiments, computational projects, student understanding of conceptual issues, ways of incorporating modern developments, issues related to energy in society, and conceptually-based ways of presenting statistical physics and classical thermodynamics.
Ising is based on the original applet written by Rongfeng Sun and Macneil Shonle. It was modified by Wolfgang Christian to incorporate Physlet inter-applet communication mechanism. The Ising applet is being released under the GNU General Public License, GPL.
The Physlet code for the Ising applet may be downloaded here.