Shelters guess a kitten's sex and are sometimes wrong, which is how a great many cats end up with a name that no longer fits. The names below sidestep the problem: the records show them going to males and females in near-equal numbers.
Where the threshold comes from
Between 35% and 65% female, on a sample of at least five sexed records. Below that floor a name carries no gender at all rather than a guess from too little evidence, which is why some names you might expect are absent.
Every count on this site is a tally of real registrations: pet licences and shelter intakes published as open data by New York, Seattle, Austin, Montgomery County, Cambridge, Zurich, Basel and three Australian councils. Popularity here is the average share a name holds across those registers, so a name common in a small city is not buried by one common in a large one. Nine of the eleven sources are North American, so read the ordering as naming in those places rather than worldwide.