Here is a really unique chainsaw, a stick shift. It is based off of the 700 series gear drive Homelite with an added 3 position gear box. Basically 3 different torque ranges. (keep in mind as you gain torque you lower RPM's). Shifting it is like any other transmission, the clutch is centrifugal so when the chain isn't spinning or at idle just toss it into another gear.  I gather it is to bring a single chainsaw for felling to limbing to bucking. "All purpose" but it added a pile of metal to lug around.