MSAFluid is a library for solving and displaying real-time fluid simulations based on Navier-Stokes equations and Jos Stam's paper Real-Time Fluid Dynamics for Games. It was inspired by the brilliant Plasma Pong.

There is a Java version to be used with processing (or any other Java framework), and a C++ version to be used with openFrameworks (or any other C++ framework). It has also been ported to Flash AS3 by Eugene Zatepyakin.

You can play with an online interactive Java version here.

(thanks to Jimi Hertz for the above video)