Hos'd Javalabs: Useful Stuff for Grave Matters

So, there's a lot of useful stuff out on the web, much of it poorly linked, so, the thing to do is to link to it.

For various reasons, I am reminded of Chris Mihos's JavaLab, a useful collection of Applets that do Gravitational Simulations of various sorts

I am particularly fond of the Surface-of-Section applet, for obscure historical reasons, but the GalCrash Applet is clearly the all time classic, and much beloved of many generations of students.