There are a lot of derivatives out there, both using Vocaloids and UTAU. Some have even been recognized by the voice bank producer companies. Also Ted (Teto’s genderbent/older brother) is an official member of the Vipperloid family. But not all derivatives are good in my opinion. Some times they seem a bit lazy and uninspired. If you look at the fanaloid (fanoloid?) wiki there are so many derivatives that are just recolors. Also there a lot of them that have the same voice. Like a lot of Miku pitch change derivatives. I might try making a derivative some day. I believe that derivatives such as Haku, Neru, and even Keko are good derivatives because they are actually unique and thought was actually put into them. I enjoy and respect those kind of derivatives. But if you just recolor Miku and change the pitch of her voice then I just see that as lazy and not very ineresting. There was one derivative I saw kind of recently who was basically a fusion of Rin and Luka. It was pretty cool and that’s the kind of creativity in derivatives I’d like to see.