They appear to be magic, see video:
Oscillating saws, OMTs, or vibration knives, move blades rapidly enough to cut into wood, metal, or even brick fairly easily. Unlike rotary saws, they don't kick or bind and are fairly lightweight/easy to handle. They aren't too costly, either and they range from $50 - $200 online.
A local installer was telling me these saws make cutting in boxes for readers or notching out frames for electric strikes super easy.
What about you? Do you use these? Which one is the best?