Snarkiverse (for those unfortunate enough not to have seen it) puts the stock KSP bodies in interesting orbits Principia simulates the Newtonian mechanics of orbits, rather than using the patched-conic approximation.
This raises several interesting questions:
+ Mun passes very close over KSC every second day. Does this give noticeable advantage to well-timed launches (like launching at high tide)?
+ Pol orbits very near Duna. Will she break up under tidal forces?
+ Eeloo orb