The Triamese was a 1965 design for an orbital launch system from General Dynamics.
The fuel of each vehicle was used in sequence to feed all of the motors via a manifold.
After the vehicle was empty it separated from the remaining active vehicles and returned to earth for a Horizontal recovery.
[1] The final stage held the cargo.
The overall concept was very similar to the 1964 BAC Mustard design and suffered the same fate.