Which cryptocurrencies deviate significantly from Bitcoin? There's been dozens of alternate cryptocurrencies but I don't believe many of them did much other than find/replace some strings.

We see Bitcoin as made up of the blockchain and proof-of-work via hashing of the next block. Have there been any altcoins that drastically strayed from this recipe?
Ripple is in my opinion very interesting that uses a very different system which isn't based on the block chain nor the proof-of-work algorithm. Rather, it uses a quite different consensus algorithm outlined here: https://ripple.com/wiki/Consensus

The only problem is that there's very little research about this concept and I can't figure out how it works more in detail without an official publication of some sort. All I can say is that it's different from any altcoin because it's based on trusting nodes that behave honestly and distrusting the ones that don't:


  If someone should be dishonest, the honest actors will notice them
  lying and can disregard their future attestations.  That is, if you lie once, you have no gain as the network doesn't care and they won't care what you say in the future.