Abstract: The present invention relates generally to fluid displacement apparatuses and methods. The inventive apparatus comprises: a housing having an interior space; a crankpin positionable in the interior space; and a plurality of articulated displacement members positionable in the interior space such that the articulated displacement members extend from the crankpin and define in the interior space a plurality of displacement zones. The inventive apparatus can be embodied as a pump, a compressor, a fluid flow meter, a stirling-type engine, a relay system, an actuator, and many other devices.