Vissian

The Vissians are a humanoid species notable for having three genders. First contact was made by the NX-01 Enterprise in 2153. (ENT: "Cogenitor")

At least one Vissian woman served as an engineer in the Federation Starfleet, serving under Captain Montgomery Scott in the S.C.E.. She was berated for him by not completing a report on a Martian time corridor generator fast enough. (The Future Begins)