Apache Cassandra ##
Apache Cassandra is an open source distributed NoSQL database designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure.
Cassandra offers robust support for clusters spanning multiple datacenters, with asynchronous masterless replication allowing low latency operations for all clients.
It was initially developed by Avinash Lakshman (one of the authors of Amazon’s Dynamo) at Facebook around 2008, to power their Inbox Search feature .
Here is a great video about how Cassandra works under the hood:
Another resource to get started is the documentation from DataStax.