Redis - Redis is an open source in-memory data structure project implementing a distributed, in-memory key-value database with optional durability.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Hazelcast - Clustering and highly scalable data distribution platform for Java
MySQL - The world's most popular open source database
memcached - High-performance, distributed memory object caching system
Microsoft SQL - Microsoft SQL is a best in class relational database management software that facilitates the database server to provide you a primary function to store and retrieve data.