Polyhedra is an in-memory database management system. It uses an Object-Relational data model, but is more strongly tied to object-oriented storage.
Object-Relational
In-Memory
Custom API SQL
https://www.enea.com/polyhedra
Polyhedra PLC
GB
1994
Enea
Commercial
C++
AIX, BSD, HP-UX, Linux, Solaris, Windows
Proprietary
https://en.wikipedia.org/wiki/Polyhedra_DBMS