An old coin which was really very different from BTC - perhaps even more than Iota or Obyte/Byteball - was Timekoin (
Github here), a PHP-based coin which is now probably dead, but I heavily doubt that the consensus model really was a "sound" model.
One could describe it as a kind of hybrid between an "obfuscated" Proof of Work system, in which the nodes competed for a "slot" to be able to mine, a Proof of "activity" system (there were multiple block rewards per block, distributed between all nodes with a slot which were continuously online for the last hours/days, and nodes that were offline several times were excluded) and a limitation of one node per IP address.
One of the more strange features was that old blockchain parts were hashed and distributed as "transaction foundations" (a kind of "macro-blocks", I think they consisted of 4096 blocks every one) to achieve additional security against a "51% long range attack" where large parts of the blockchain were faked, so it wasn't a traditional blockchain where all blocks are independent. That sounded good back then for me when I was new to blockchains, but now I think this measure should have limited effects on security. At least, it has the same problem than "decentralized checkpoints" in PoS coins (if there are different "foundations" in competition, then the network could get fragmented).
