Riak is a distributed NoSQL key-value data store that offers high availability, fault tolerance, operational simplicity, and scalability. In addition to the open-source version, it comes in a supported enterprise version and a cloud storage version. Riak implements the principles from Amazon's Dynamo paper with heavy influence from the CAP Theorem. Written in Erlang, Riak has fault tolerance data replication and automatic data distribution across the cluster for performance and resilience.
Riak is licensed using a freemium model: open source versions of Riak and Riak CS are available, but end users can pay for additional features and support.
Riak has a pluggable backend for its core storage, with the default storage backend being Bitcask. LevelDB is also supported.