The second question/idea is a bit far out: Are there any "open source"
projects? It's obviously extremely difficult to exchange parts of
airplanes across the web, but people could develop something together
and everyone builds his or her own plane from the plans that come out
of this (and even those not building could bring in their expertise).
I know this is not computer software (even for a model airplane it
could work well), but has something like this been undertaken? Is it
feasible?

Oliver

If open source airplane designs worked like open source software I
wouldn't go near the end product -- because my life would depend on
it.

And if I ever find out open source software is running aircraft
systems I won't fly on it. But of course that will never happen.