What aircraft has 3 propeller engines?

A 3 propeller engine airplane is called a tri-motor. The Ford tri-motor was a popular commercial airplane in the early 1930s. It was replaced by the DC3.

During the 1930's 3 engine aircraft were quite popular and there were many of them . The most built was the German Junkers 52. After WW2 they lost popularity and about the only ones I can recall are the De Havilland Drover, built by DH Australia and the Short Trislander, both built as short haul airliners.