They are usually called rovers, unless they actually fly. I cannot name any single atmospheric flight on another planet, only controlled plunges.

The Vega-1 and Vega-2 balloons operated for more than 46 hours in the atmosphere of Venus as part of the Soviet Venera programme [0]

[0] https://en.wikipedia.org/wiki/Vega_program

Everyone forgets about that program, and it was incredible stuff.