The father and son team of Lance and L. J. Nybye have come up with a wonderful line of mechanical add-ons for common light-switch covers. The mechanisms are typically cut with a laser from high-quality plywood and finished off with brass hardware. Additional decorations are engraved/burned into the parts with the laser.
From the online shop:
These mechanical light switches transform an ordinary appliance into the perfect flourish for your secret library, steampunk chalet—or wherever your imagination lives!
The mechanical switch covers install easily over a standard switch plate using the existing screws. In addition to the excellent lever-based switch shown in the video, they have a couple of other lovely designs.
Here is their one based on planetary gears...
And another design based on the rack and pinion mechanism...
Here is where you can get these mechanical switch-plate covers.