PostgreSQL is open-source relational database management system.
It is a sufficiently stable and reliable solution, also for highload. Support partitioning and replication out-of-the-box or with extensions.
Besides general data types postgres support geometry types (points, circles), GIS types (coordinates, polygons), and user-defined types. Some featudes from no-sql databases such as json and array are also supported.
LISTEN-NOTIFY it can be used as message broker, as backend for background workers or as notification system (not recommend for highload).
Postgres is fast. In a single core it can, per second:
Official site: https://www.postgresql.org/