You say this jokingly, but onboard software is a feature in some satellites right now. The ability to push and update applications that run directly on the vehicle instead of needing a downlink to a ground processing station is on the roadmap for increasingly compute expensive operations, but still pretty basic right now. I don't think there are any that will run untrusted code from arbitrary developers, though. That's a pretty steep risk.
I'm having trouble finding any unclassified examples of this, but you can read about TechSat-21, which was supposed to be a proof of concept back in 2004 but the program was canceled because of cost overruns: https://ml.jpl.nasa.gov/papers/the_techsat-21_autonomous_sci...