The F-82 was the last propeller-driven fighter acquired in quantity by the USAF. It appears to be two Mustang fuselages on one wing, but in reality it was a totally new design. Its purpose was to provide a fighter carrying a pilot and co-pilot/navigator to reduce fatigue on long-range bomber escort missions. A lot of photos this aircraft can be found in the link:
http://aviacaoemfloripa.blogspot.com.br/2011/03/north-american-p-82f-82-twin-mustang.html