If you believe in Astrology, Zodiac, and Sun Signs and your child is born either a Sagittarius or Pisces, which are ruled by the planet Jupiter, you could name your child Callisto after one of Jupiter's moons. I'm pretty sure this is one of those names that could fit either a boy or girl and it's a pretty unique name that a child, no matter the gender, can grow up with just fine. Also, the most famous show, Xena, in which this name is used is very old by now and not everyone watched it so it's pretty much safe from too many people making the association. If used on a girl, you have the opportunity of a pretty nice nickname possibly of Calli, or Cal for a boy!Also, if you happen to be a Xena fan and want to quietly but proudly show it, naming your child Callisto is a nice, subtle way of doing that and fellow Xenites will respectfully recognize you for it! Xenites Unite!
Callisto was a character, played by the actress Hudson Leick, in the series 'Xena: Warrior Princess' and made appearances in its parent show, 'Hercules: The Legendary Journeys'.
Callisto of Marvel Comics. She was the leader of an underground tribe of mutants called the Morlocks, until she lost that title in a duel with the X-Men's Storm.