PostgreSQL 
*Platform: Windows, Linux, and macOS. 
*Languages: PL/pgSQL, PL/Tcl, PL/ Perl, and PL/Python. 
*Cloud version available: No
 
PostgreSQL or Postgres was built to be the successor to Ingres, a database software developed by the folks over at the University of California, Berkeley. Like most relational databases, PostgreSQL supports ACID (Atomicity, Consistency, Isolation, Durability) features and is designed to help build applications that are fault tolerant and for managing large data sizes. PostgreSQL supports different  data types such as primitive, structured, document, geometry, etc. Another interesting feature is the support for international character sets which makes it popular for building applications that are meant to support languages, aside from English. Also, like  most databases, it also supports client-server network architecture.