There is a new, improved version at This Link with substantially expanded capabilities including critical phenomena. This old version is kept here mostly for archival purposes. Most users will want to switch to the new version.
The applet appears below but you will probably want either to look at the Instructions (they'll pop up in a new window), if you are already familiar with the basics of phase equilibria, or the Tutorial for a step-by-step introduction to all the concepts involved.
This example has four phases (A, B, C, D; B is the most "liquid-like") and includes an invariant point, several univariant reactions, coincidences, and singular points. You might want to begin with a simpler example with only two solids, a liquid, and one eutectic reaction.
Send suggestions, whines, and flames to Paul Asimow.