I've developed my own software for converting STL to GCode (hence the name of my milling machine - STLCutter).

It's not too difficult; my challenge was that I needed a large object cut up into a number of blocks, and each block is cut individually.

I've also written a number of algorithms that are designed to give different qualities of cut depending on the complexity of the object being cut.

For example, the original algorithm would do a scale model cut of the car I'm building in just over 2 hours - a new algorithm which is more suited to smooth objects has cut this to 28 minutes. There's one other algorithm which I'd like to get working, but it's a very complex algorithm to work out.

The accuracy I've put into it isn't terribly high (1mm), but it's just numbers to the computer - higher resolutions can be easily created.

If your brother wants to contact me, send me a PM - I can give some help if he needs it.

The only slight thing is that I've done my software in Mac OS (with Objective-C), since it's my main platform (at home) for development. However, it originated in standard C on a BSD box.