In 1957, engineer Pierre de Valroger presented the coupling of three RR/Bristol Viper engines (see).

“Exterior of the Valroger engine”

In this engine grouping, the exhaust gases from each engine discharge onto a large-diameter turbine that drives the propeller shaft through a reduction gear, which, curiously, is located at the rear.

“Arrangement of the three Vipers”

And more clearly in the diagram shown below. It was christened the “Tri-Viper”.

“Tri-Viper”

There isn't any known application. It is assumed to be an engineering exercise. Original, though.