Alter/Ego (アルター・エゴ) is a real-time voice singing synthesis platform (VSTi/AU/RTAS/AAX64 plugin) by Plogue Art et Technologie, Inc.
Alter/Ego has the same work-flow as chipspeech but is intended to host voice technology that is not strictly vintage. In other words, post-1990 published research.
It is specially tailored for musical needs – simply type in your lyrics, and then play on your MIDI keyboard. It's a true synthesizer, the sound can be extensively modified for easy and expressive performances.
Voice banks come in various styles and licenses. Bones is the latest bank available and is also free.