From another place:

My house was built in the late 50's with everything electric made by GE. It had a GE heat pump, an electrostatic air cleaner that looked like it was from a nuke plant, even GE wire nuts! It still has the 24volt latching relay system for the lighting. There are 18 circuits for the output, directly from the relay to the lights / outlets. All over the place I have 3 wire low voltage runs to rocker switches that control the relays. While this may seem a nightmare, the whole thing works very well. The relays are still used in big commercial buildings , still available, and everything is pretty robust. Because the control can be easily ganged I have the ability to turn on the upstairs hall light from within each bedroom and downstairs so it is the equivalent of a 7 way switch. From the master bedroom there is a rotary selector and rocker to control every circuit on the system.

Heat pumps, electrostatic air cleaners, remote control lighting are we returning to the future;-)