Ever wanted to get the feel of what it’s like to be in a sub? Better put, a German sub during WW2? Danger from the deep is your best bet.
“Danger from the Deep (known as dangerdeep or DftD) is a free (as in free speech), Open Source World War II german submarine simulator. The program and source code is available under the GPL license and most of the artwork/data is released under a Creative Commons license (Attribution/NonCommercial/Non-Derivative works).”
With DftD, you get to travel back in time to the WW2 to experience a German sub and how it works thanks the to the games advanced simulation. It is multiplatform and is partly based on the open graphics library OpenGL thus should reasonable easy to port.
It is available for download for Windows, Linux and Mac OS X.