Knoppix uses aufs2, this is like a more improved version of unionfs (according to kl522 I don't know enough to compare both of them).
You can specify branches and mount them over eachother and also specify the operations that can be performed on them WITHIN the unionfs space.
So say I have a writeable directory A and another B, then I can mount A over B and say that A is read-only while in fact it is read-write.

This way I can make it save all unionfs changes to the ramdisk and also run another script to bypass the unionfs read-only limitation and that script exists, it's called "aubrsync".

This all sounded too good to be true and in fact it is there is one catch and that is that aufs-tools need to be installed and be the same version as the one that was used to patch the kernel. Too bad I have no idea what that is...

I am currently trying to compile the newest version without succes, I'll continue my quest tomorrow