Porteus

What exactly happens when two modules contain the same packages? Does it just overwrite the files?

files from module activated later will overwrite files from previous modules. please read aufs manual if you are interested to go deeper into this topic:
http://aufs.sourceforge.net/aufs2/man.html

cheers

It's like a birthday present wrapped by your annoying aunt, only the wrapping paper is transparent.

Each module activated is another wrap around your present. Any words (files) on underlying wrappers are still visible but ONLY if not the upper most wrapper doesn't have a word (file) covering the one below. If there IS a word covering the one below then you only see the word on the upper most wrapper.

This is of course very over simplified, but then so is my annoying aunt.

I do like the wrapping analogy