-> I don't know if it's quite what you're thinking about, but there 
-> are a pair of moons at Saturn that are near enough in the same 
-> orbit at the same place, that they interact and swap orbits. 
  
Yes. I've heard of those. 
  
There is also an asteroid that pretty well shares Earth's orbit. Every 
now and again, the asteroid comes up from behind Earth. Earth's gravity 
attracts it, so the asteroid gains orbital energy. This causes it to 
*slow down*, so it drops back behind Earth. Eventually, it drifts right 
around so it approaches Earth from ahead. It then loses energy, and 
speeds up. This cycle continues indefinitely. 
  
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