Majority of all altcoins have it own unique features, most just useless.
Well, I believe most of them actually don't. At least, they have too much in common. It's true they are sort of adjusted to very different things from game items to advertisements. Yet I don't think it really counts as unique features.
OP, I would like to name the coin I mention a lot, which is the most unique coin I've ever seen. I am talking about IOTA. It's uniqueness starts from the fact that it's not a blockchain-based currency. It has a whole different tech called the tangle. It's a graph with knots instead of a chain with blocks. It's kinda hard to understand deeply what it is all about, but it makes the fees free morever, no mining or pos possible and transactions instant.