Lawrence Lessig has just released the second version of his well/known
book "Code". It is CC-BY-SA and can be bought/downloaded for free at
http://codev2.cc/
Two reasons I mention this here:
1. It was (re)written using a wiki
2. At the beginning, it says:
"Code version 2.0
TO WIKIPEDIA,
THE ONE SURPRISE THAT TEACHES MORE THAN EVERYTHING HERE."
Feeling good,
Magnus