On some micro RC vehicles, in place of servos to control the rudder or elevators or steering you'll find one or more lightweight actuators. In the case of actuators on micro RC airplanes, they act like little hinges on the rudder or elevators. Move the stick that controls the rudder and tells it to turn right and the receiver sends a signal to the actuator that makes it flick to the right. Move the stick back and the actuator and rudder returns to neutral. One actuator controls one movement. For left rudder control, the plane would need another actuator.
Actuators don't provide the same precise control as servos because they are either on or off -- no incremental movements -- but their small size and light weight makes them useful in micro vehicles such as tiny infrared cars or the tiniest of RC airplanes where traditional or even micro servos would be too large and heavy.