Three phase systems - are there any single phase devices that are connected between two phases instead of between one phase and neutral?
In the USA, some residential and commercial services are supplied with 120/208 volt service. The 120 V phase to neutral is used for standard wall receptacles and lighting. Phase to phase 208 V is used for single-phase kitchen stoves, water heaters, clothes dryers and motors in heating and air-conditioning units. Small single-phase motors are widely available for 208 volts.

In the rest of the world, where 220-230 V is supplied for wall outlets and lighting, the phase to phase voltage is 380-400 volts. Single-phase motors for that voltage level would be quite unusual. It seems unlikely that other loads would be served at that voltage, but it is certainly possible.