The bloom filter could be used in a similar way, you have X hash functions used and Y total bits, so for a bloom filter with Z bits set you anticipate N unique

The bloom filter could be used in a similar way, you have X hash functions used and Y total bits, so for a bloom filter with Z bits set you anticipate N unique items were hashed. Probably not as good as the HyperLogLog in terms of memory space / % error, but there you go.