Boolberry uses an algo named Wild Keccak. This is refered to as a blockchain based POW. How does this work?
There is a high-level description of this algorithm at http://cpucoinlist.com/cryptocurrency-algorithms/wild-keccack/ which reports as follows:
Wild Keccak is a Keccak hybrid which uses blockchain data as scratchpad. After each Keccak round, pseudo-randomly addressed [state vector used as addresses] data is taken from scratchpad and XORed with state. Calculating each block PoW usually hits about 1100 randomly addressed reading of blocks by 32 bytes.