I'm happy to announce the release of "Verlet Well", a 2D RBD engine for Java 2 SE. Please send e-mail to firstname.lastname@example.org
if you're interested in purchasing the engine.http://www.geocities.com/bpj1138/VerletWell.html
The engine comes as source code to the applet above. You'll have to modify the code to suit your needs, but the basic framework is there. As you can see the engine is capable of handling resting contact which is one of the strengths of the Verlet integrator. In addition to that it can handle hinges and other constraints without much programming effort. Incredibly, the entire source code to the applet is only 776 lines long which includes applet initialization, graphics, user input, threading and other support structures. The physics code is only about two pages long. Finally, take a look at your CPU usage while running the applet, I think you'll be pleasantly surprised.
Thank you for considering "Verlet Well" as your physics engine, and I wish you all happy hacking.