Gerris Flow Solver
Gerris is a Free Software program for the solution of the partial differential equations describing fluid flow. The source code is available free of charge under the Free Software GPL license.
Gerris was created by Stéphane Popinet and is supported by NIWA (National Institute of Water and Atmospheric research) and Institut Jean le Rond d'Alembert.
A brief summary of its main features:
Have a look at the introduction for more information.