Many light aircraft have variable pitch props, otherwise known as constant speed units (CSU). Nearly all light twins are CSU equiped.
In the cockpit, you control the CSU with a pitch lever/s, usually located between the mixture and throttle lever/s. The CSU operates by using a governor which regulates the speed of the propeller. Moving the pitch lever sets RPM and does not directly set the pitch of the propeller. The governor then maintains the desired RPM by continually adjusting the propeller pitch.
Not all variable pitch props can be feathered. However, most found on multi engine aeroplanes can be feathered. The prop is driven into the feathered position either by oil pressure or counter weights.
It is almost impossible to explain how all this works without diagrams and a lot of time.
Yes a DC3 has variable pitch props, and I have no idea about reverse on piston engine aeroplanes. I can't think of any that do, but I'm sure there is some whacky Russian machine out there that does have it.
Hope this helps.