Apache Cassandra is a free and open-source distributed database.
It is a Java-based, highly scalable, eventually consistent, wide
column store. Cassandra database clusters are masterless with no
single point of failure. Replication can be configured across
multiple data centers.

Originally influenced by Dynamo and BigTable, Cassandra was initially
developed at and open sourced by Facebook before becoming a top-level
Apache project.

The CQL query language offers SQL-like data access and management.
Drivers are available for a number of languages.