LiveGraphics3d

We've just heard (belatedly) about this really nice Java Applet called LiveGraphics3d that comes from the Mathematica-using math community. It seems relatively simple to use, is well documented, and while it has limitations, it could still be very useful for displaying things like cosmic ray showers, galaxy simulations, and results of machine learning algorithms. What's quite amazing is that you can define lines and surfaces using equations. It can handle at least a few thousand points quite well, too.

Martin Kraus, the creator, has some nice examples of impossible objects :