Riak (pronounced "ree-ack" ) is a distributed NoSQL key-value data store that offers high availability, fault tolerance, operational simplicity, and scalability. Riak moved to an entirely open-source project in August 2017, with many of the licensed Enterprise Edition features being incorporated. Riak implements the principles from Amazon's Dynamo paper with heavy influence from the CAP theorem. Written in Erlang, Riak has fault-tolerant data replication and automatic data distribution across the cluster for performance and resilience.

Riak has a pluggable backend for its core storage, with the default storage backend being Bitcask. LevelDB is also supported, with other options (such as the pure-Erlang Leveled) available depending on the version.

Riak was originally developed by engineers employed by Basho Technologies and maintained by them until 2017 when the rights were sold to bet365 after Basho went into receivership.

All versions of Riak are now entirely open-source and free, and include the extra features that Basho charged license fees for.

Basho operated a freemium model, wherein they provided free versions of Riak in the form of Riak Core, Riak KV, Riak CS and Riak TS but made their money from licensing more advanced features and SLA-based support. The extra features from the Enterprise Editions have since been integrated into the open source version of Riak KV, as of Riak KV release 2.2.6. and Riak CS 2.1.2

riak_core is the distributed systems framework that underpins Riak, forming the foundation for all Riak versions. It is being maintained as part of Riak.

riak_core_lite is intended for general use as a base for creating distributed systems.

Riak KV is a distributed NoSQL database designed to deliver maximum data availability by distributing data across multiple servers, meaning that if one client can reach one server, it should be able to read and write data. KV went through a few names in its lifetime, starting as Riak then Riak DS (for Data Store) and finally Riak KV (for Key-Value).