Redis
Updated: 04/26/2017 by Computer Hope
Redis, also known as the Remote Dictionary Server, is NoSQL server software released in 2009. It is a key-value store that serves data structures to applications. It can serve strings, lists of strings, sets of strings, sorted sets of strings, and hash tables. Because Redis stores its data in memory, it has performance benefits over traditional databases that must write all data to disk before altering the database contents. It's not ideal for data such as financial transactions but excels at persistent session information and user messaging.
Redis is open source and free to operate on your server. It's also offered as part of many cloud services such as Amazon Web Services and Rackspace's ObjectRocket.