I was surprised to find that New Horizon is using Nucleus but I guess it makes sense since it was developed largely outside of the NASA-JPL west coast mafia (on

I was surprised to find that New Horizon is using Nucleus but I guess it makes sense since it was developed largely outside of the NASA-JPL west coast mafia (only slightly joking...). JPL has been using Wind River's VxWorks RTOS since the mid-1990s including on missions like Mars Pathfinder, the Mars Rovers, and most recently on the Mars Science Lab Curiosity. I don't have an authoritative list but if two missions running VxWorks are on opposite sides of the solar system (very likely) or on a slingshot out on the opposite side of Mars (less likely), VxWorks might take that most wide spread crown. It's definitely present on at least half a dozen active missions in the solar system.