This is similar to, but more complicated than Momentum, which asks for a simple hash collision.
I read that Momentum was only used in the initial phase of BitShares. Now they use a form of proof of stake. Are there any other altcoins that have used or are using Momentum? I also read some of the Momentum whitepaper, but not enough to understand how the algorithm works.
It was and still is used in Protoshares (nowadays also called Bitshares PTS).
Not used anywhere else.