Here in the UKin the 1970's Black & Decker use to sell various "attachments" to turn a standard electric drill into various different sorts of power tools. One of the "attachments" that you could get was a "circular saw attachment" that turned a standard electric drill into a "circular saw". I'm not sure that it would meet modern safety standards nowadays but people didn't worry too much about that then. I remember that my father "burnt-out" multiple electric drills because the motor wasn't really powerful enough to power a circular saw.