What about HyperLogLog? Seems to fill the same niche http://antirez.com/news/75

Hey Alexey. Hyperloglogs are similar in the sense that they hash the input first, but that's where the similarities end. While hyperloglog uses a log of the number of longest strings of zero in the hash to estimate the cardinality of a set (number of unique items) without knowing at all what those elements were. Bloom filters store the hash(es) as a representation of the element.
Or in other words: Bloom filters test for presence of an element in a set. Hyperloglogs estimate the number of unique elements in a set. Hope that helps to clear things up.