Business System 12
An RDBMS designed to be strictly relational, unlike SQL. An important example of the model independence of a particular implementation such as SQL.
LEAP
A non-SQL relational database using algebra. [Free software, GNU GPL]
Multics Relational Data Store
RDBMS running under Unix's parent, Multics. Released June 1976, believed to be the first relational DBMS offered by a major vendor: Honeywell.