PostgreSQL

PostgreSQL is one of the world's most widely-used object-relational database management system (ORDBMS). The technology gained huge popularity due to to the extendability, high security and ability to use multiversion concurrency control (MVCC) to efficiently handle various workloads, ranging from single-machine apps to heavy-duty web services with thousands of concurrent users. PostgreSQL is also compatible with major open-source and proprietary DB systems.