A really simple 2D physics engine in Java tossed together in two very short evening sessions.
Note that this was built to illustrate a few points only, and not to build an actual physics engine. It's currently rendering using Swing because I didn't have any energy to look anything else up, but it shouldn't be that much work to get it to render with something like OpenGL (if a renderer is already in place, that is).
It doesn't handle anything except basic gravity. There's also no real optimizations, but rather we're brute-forcing our collision pairs (meaning a lot of redundant checks in the engine).
Again, solely built to demonstrate some basic physics engine concepts. If you feel like something in here is useful, feel free to nab it and use it in other software. Released under the MIT license.
You're welcome to submit PR's, but I'll most likely not continue working on this :)
Assuming you have Gradle installed:
gradle run
And that should pretty much do it.