Mohr's Circle for Plane Stress
I got this applet from someone at Virginia Tech who was kind enough to make the source code available. I haven't gone through the code myself so cannot attest to its accuracy; that'll be your job. I expect it should be correct but if you find that it's not, please email me and let me know exactly what the problem seems to be. I did notice that the creator was unable to format the numbers. Contrary to most tasks in JAVA, formatting is not done as easily; if you know how to do it, please let me know.
A related item can be found at the
West Point Civil & Mechanical Engineering website. They post a windows application that you can get and put on your PC. Once you have it, you can enter values as below and then annimate the rotation through 360°.