Rowan - love it for a boy, like it for a girl. I've known 4 males and 2 females with this name.
Wren - not keen for a girl. Not sure it's a boys' name at all? Never met a Wren at all though.
Robin - love it for a boy or a girl but would spell Robyn for a girl. I've known 1 boy Robin and 3 girl Robyns. Never met a girl Robin.
Frankie - not keen on it for a girl, don't like it at all for a boy. I do love Francesca but not keen on Frank, Francis or Franklin.
Stevie - like it for a girl, it's 'cool and funky'. Don't like it for a boy. I know 1 female Stevie.
Sidney - like it for a girl but spelled Sydney. Don't like it for a boy, it seems too middle aged although I know it's trendy now. Only ever met 1 girl Sydney and no boys.
My rankings would be very different for girls and boys:
girls - Robin, Stevie, Rowan, Sidney, Wren, Frankie
boys - Robin, Rowan, Frankie, Stevie, Sidney, Wren
As gender neutral names go, I like the surnamey kind of names which seem to have become very popular for girls but were originally male. I don't know if they're truly gender neutral or just female now. Names like:
Addison, Aubrey, Avery, Brodie, Bailey, Colby, Dakota, Eden, Erin, Fallon, Harley, Hadley, Jocelyn, Kennedy, London, Madison, Morgan, Peyton, Quinn, Riley, Sutton, Spencer, Taylor