Majordodo: Distributed Resource Manager uses Apache ZooKeeper and BookKeeper. http://majordodo.org/
Huawei: Uses BookKeeper as shared storage in Namenode HA.
HubSpot: Uses Bookkeeper in production at the core of its (custom) write-ahead-log service.
Twitter: Uses Bookkeeper as the core storage backend for replicated log service serving use cases like search ingestion, self-serve pub/sub system and strong consistent operations on distributed database.
