There was Wei Dai's b-money, Hal Finney's reusable proof of works (RPOWs), and Nick Szabo's Bit Gold. Bit Gold was the most similar to Bitcoin and only differed in that 1. influence was determined by no. of nodes rather than mining power which made it vulnerable to Sybil attacks, and 2. the difficulty was not adjusted as mining power increased which necessitated the bundling of coins from different time periods in order to maintain fungibility. Of the three proposals, only one was actually implemented in code and that was Finney's RPOWs. There might have been others as well and the early cryptocurrency proposals shared much in common with attempts to put a cost for sending out emails in order to combat email spam which was a problem that a lot of other people were working on at the time.