Adds a directional-actuator that conditionally toggles the activity of an adjacent object. The gui of the entity is the same as for any inserter. You can set conditions by circuit-wire or logistics.
Some examples are deactivating/activating:
Assembling machine, oil refinery, chemical plant, labs, radar, steam-engine, boiler, heat-exchanger, steam-turbine,
nuclear-reactor (heat is still distributed through it),
Tank, pipe, (still gets fluid in, but no longer out)
beacons, lasers (still drain energy, might make sense only if adjacent machines use loads of energy and they don't need to receive speed boost all the time...)