Just released a new version the other day for beta testers. The new features you'll see are:
The revolute joint is, of course, a very common component in multibody software, mathematically analogous to a hinge. You can define a rotation axis either as one of your basis vectors, or specify components in multiple basis vectors. The example at the right shows a rotation about the vector 0.707 i + 0.707 k.
Spring graphics now use vector drawing commands, instead of the previous implementation where they were from pre-generated .png images. Should look a bit cleaner, and possibly have a little lower rendering overhead.