Like MS SQL Server, PostgreSQL is a full RDBMS. It's a hard core enterprise system that goes after drop in replacement with Oracle DB. Pretty much any enterprise software using a database lets you select between PostgreSQL, Oracle, Sybase and SQL Server if not many more like MySQL, MariaDB, DB2, etc.
MySQL is focused on lightweight web applications so is tuned differently than the others. PostgreSQL is the new darling for enterprise app development. It's old but really good.