An active DBMS developed at the University of California at Berkeley by a team led by Michael Stonebraker (1986-1994). Postgres was later taken by Illustra and developed into a commercial product, which in turn was bought by Informix and integrated into their product, Universal Server.
PostgreSQL is a further development of the original POSTGRES code as a free software alternative to commercial DBMS vendor offerings.
[Details? Reference? Relationship to Ingres?]