As I am sure you know by now STOL stands Short Take Offs and Landings. Many of your “regular” small aircraft can be equipped with a STOL kit to help them perform better on the slow end of the flight envelope. Many of these perform better on the bottom end but don’t suffer too much on the top end. Like the Cessna 182 and 421 can both be set up with a STOL kit by Robinson for example to allow good low speed flight characteristics but that kit doesn’t necessarily affect negatively the top end characteristics.
A purpose-built STOL can be very impressive and is many times slower for the amount of horsepower and fuel used. Of course you can land them in places that are unbelievable. On a windy day they can come down rolling backward if you wish to scare the passengers. Maule at www.mauleairinc.com makes some very impressive performing 4 place aircraft. The last one I saw was a little rough around the edges from the factory but would knock your socks off coming off the ground.