Like SunnyWolves said, Deepvocal and Niaoniao (although it is hard to find Niaoniao resources in English). Talqu was also pretty popular a few years ago- Teto and Ruko have voicebanks for it.
If you're REALLY confident in your CVVC otoing skills you can try messing around with the V3 devkit, but you can't distribute the voicebank. The V1 devkit is also available and, since Vocaloid 1 is officially abandonware, you could attempt to make a V1 and distribute it.
Mako Nagone has a custom text-to-speech software called Mikovoice made specifically for her.