FlockDB is an open source, distributed, fault-tolerant graph database created by Twitter to store and analyze relationships between users, for example, followings and favorites. It is designed for rapid set operations and very large adjacency lists (20,000 writes and 100,000 reads/second), and it is not intended for graph traversal operations. Since it is still in the process of being packaged for use outside of Twitter, the code is still very rough and hence there is no stable release available yet.