If when running ./configure you got lines looking like
checking for mpicc... yesthen you don't have anything else to do. Otherwise, you need to make sure that you have MPI installed and that the mpicc command is in your PATH.
For running the code in parallel, you will have to wait until I have written the next chapter of the tutorial...
Yes, more generally it should support any MPI implementation which defines a working mpicc command accessible in the PATH.
% ./configure --disable-mpi
Certainly not a native Windows version (Gerris relies on features found in professional operating systems) but one should be able to compile and install it on Windows using cygwin.
Gerris also runs on MacOSX.
My personal advice would be ``why use Windows?''
I have chosen the ``classical'' point of view that, if the general description of the arguments and of what the function does (given just before the body of (almost) all the exported functions) together with the code in the function itself does not clearly describe what the function is doing, then this is a problem with the code itself not with the documentation. A counter-example of that would be a very long monolithic code described by comments every few lines.
Also, from my personal experience, working with a number of research and commercial codes, I would consider Gerris to be fairly well documented. The code is also quite modular, so you shouldn't (hopefully) need to go through all the 16000 lines of code...
Of course, I would be glad to address any detailed problem you may have (unclear documentation etc...)
No. Gerris is already object-oriented (with class inheritance etc...), see the tutorial for an example of how this works.