Answering this question by listings would result in the page being constantly outdated.
Do note that genderswaps are not official nor are they acknowledged by the official companies. Also the genderswapping of characters varies greatly among the fandom, at any point a gender variant can change appearance drastically depending on the artist drawing it. However, there are moments when a consistency for a character happens and the fandom appears to accept a specific appearance for that character.
- The most popular male genderswap is Hatsune Mikuo, a male version of Hatsune Miku. Mikuo is an unofficial Vocaloid by the fandom, drawn by various artists who change his look constantly. He usually (if always) looks like a masculinized Miku with shorter hair and no skirt.
- The most popular female genderswap is Kaiko, a female version of Kaito. Kaiko is an unofficial Vocaloid by the fandom, and although drawn by various artists there seems to be a consistent appearance for her. Primarily she has short hair and wears a dress and boots.