Amazon Polly turns text into lifelike speech, allowing you to create applications that talk and build entirely new categories of speech-activated applications.
Element is an audio plugin host, modular synth, effects rack made for live performance. Audio Plugin Host Features Third Party Plugin Support (AU/VST/VST3)
Helm is a free, cross-platform, polyphonic synthesizer with a powerful modulation system. Helm runs on GNU/Linux, Mac, and Windows as a standalone program or as a LV2/VST/VST3/AU plugin.