1. the first sourcecode that prevents file copying while allowing public access.
Bitcoin's innovation is not that it prevents double-spending. That was invented by David Chaum in the 1990s and formed the basis of DigiCash. Nor is "mining" new; that's from Hashcash in the 1990s. Bitcoin combines the two concepts. The end result is a lot like Digicash, but distributed.
i actually re wrote that above in response to 2112.
part of the difficulty of Bitcoin is figuring out just what it is and how best to apply it. i've been thinking about this all day and i think that Bitcoin is the first system that allows the public distribution of a file (blockchain) that only allows modification according to a predefined set of rules. any attempt to modify this file outside of these rules will be rejected.