Robot Choir is a macOS app in development which allows a Mac to sing along to a tune entered by hand, from an UltraStar file, or using a MIDI device. Or, if you prefer, it’s how I keep Jurple, Zorange and Quilver occupied so they don’t take over the world. I have been using Robot Choir for my own purposes for many years, and gradually improving it, but have yet to give it a good enough user interface for general use. Songs I have recorded using the Robot Choir can be found on my Creative Output blog. The best recordings are on their album, Too Many Robots:
spondee.software 