Did you know that if you were standing on the near side of the Moon, and for your mass of 80kg and weight of 785N on Earth, due to Moon's lower gravity, you would not feel being heavier than 13kg (130N)? You knew? Ok, did you know that Earth's and Moon's gravities combined gave you different weight on near and far side of the Moon? Slightly yes, but true. Earth and Moon are relatively small celestial bodies but this difference goes even higher if you move from the Moon to the Io or Europe for example as they are also tidally locked by Jupiter just like our Moon is locked by Earth. This would most definitely not help mountains on Avatar's Pandora to float but still, within right conditions and with presence of large mass(es) nearby, considering appropriate composition of the ground I am sure there are solar systems out there with strange conditions to live with, to say the least. "If I have seen further it is by standing on the shoulders of giants” - Isaac Ne