The major predecessor of bitcoin is Wei Dai's b-money (1998), which is mentioned in the bitcoin paper. The proposal is online on weidai's site:
http://www.weidai.com/bmoney.txtOne difference of b-money to bitcoin is how Dai thinks about servers. Because Torrents didn't exist, he naturally thought of a central datastore as a server. What is very interesting is that here the server has partly the same function as a bitcoin node, partly different functions - the server has a balance attached to it, but this balance acts as an insurance against misconduct.
In the second protocol, the accounts of who has how much money are kept by
a subset of the participants (called servers from now on) instead of
everyone. These servers are linked by a Usenet-style broadcast channel.
The format of transaction messages broadcasted on this channel remain the
same as in the first protocol, but the affected participants of each
transaction should verify that the message has been received and
successfully processed by a randomly selected subset of the servers.
Since the servers must be trusted to a degree, some mechanism is needed to
keep them honest. Each server is required to deposit a certain amount of
money in a special account to be used as potential fines or rewards for
proof of misconduct. Also, each server must periodically publish and
commit to its current money creation and money ownership databases. Each
participant should verify that his own account balances are correct and
that the sum of the account balances is not greater than the total amount
of money created. This prevents the servers, even in total collusion, from
permanently and costlessly expanding the money supply. New servers can
also use the published databases to synchronize with existing servers.
