There are cranks where each arm is independant, if you stop moving your left leg, the right can still pedal. Its a training tool for better spin.
There are cranks with a built-in step-down transmission to engage a lower gear. The cranks can spin faster than the chainwheel.
There are gearboxes that lie between the cranks and the chainwheel (G-BOXX), these are usually based on Rohloff style gear mechanisms.
Adding cogs and other bits adds weight, complexity and reduces efficiency so these are strictly niche products.