JOS

Java Objects Simulation (JOS) is an N-body simulation system written in Java.

The idea was to have a simulation system which can use different interaction laws to calculate the force emerging between the objects.
Current version implements only Newton's law.
For GUI it uses Swing and Java 2D Graphics.
GPU version (master branch) does not use Z coordinate of the objects. This is done for faster calculations but can be easily changed.
CPU version (arbitrary_precision branch) use Z coordinate.
Current visualization is 2D only.
Aparapi library is used for GPU computations.
The CPU version (jos-cpu.jar) introduces an abstraction for numbers which allows you to choose which implementation to use: primitive type double, common BigDecimal or arbitrary precision ApFloat.
If you need precise numbers try ApFloat. It should be faster than BigDecimal.
You can save/load simulation properties using JSON format.
You can also save/load the simulation run itself and play it later.