Viking 1
Viking 1 was the first of two spacecraft (along with "Viking 2") sent to Mars as part of NASA's Viking program. On July 20, 1976, it became the second spacecraft to soft-land on Mars, and the first soft lander to successfully perform its mission. (The first spacecraft to soft-land on Mars was the Soviet Union's Mars 3 on December 2, 1971, which stopped transmitting after 14.5 seconds.) "Viking 1" held the record for the longest Mars surface mission of days (over 6¼ years) or Martian solar days, until that record was broken by "Opportunity" on May 19, 2010.
CubeSat
The May 2018 launch of the "InSight" stationary Mars lander included two CubeSats to flyby Mars to provide additional relay communications from "InSight" to Earth during entry and landing. This is the first flight of CubeSats in deep space. The mission CubeSat technology is called Mars Cube One (MarCO), each one is a six-unit CubeSat, 14.4 inches (36.6 centimeters) by 9.5 inches (24.3 centimeters) by 4.6 inches (11.8 centimeters). MarCo is an experiment, but not necessary for the "InSight" mission, to add relay communications to space missions in important time durations, in this case from the time of "InSight" atmospheric entry to its landing.