FLIT is a (F)PhotoLITography optics simulation application.
Program have GUI and computation as separate parts. GUI is writed in python for GTK2 widget set, and main part is writen in C.
Mask is described by a vector file, that is rasterized with required resollution.
Currently application working ONLY IN LINUX enviroment. It doesn't have installer, have bugs, etc, but it worked. It REALY compute a diffraction pattern of light in photolithography device. Image of the mask pattern projected into a destination using short length ligth waves. All parameters can be changed.
Although application currently run only on linux, the porting is actually very easy. C part probably should compile on MinGW or cygwin after some small changes, or even without them. Mail me if you have some serious intention using it on windows.