Voicemod

Voicemod sits between your microphone and everything else on the machine, so any application that can pick a capture device — Discord, OBS, a game's voice chat, a browser call — can use a transformed voice without knowing anything about it. Effects are applied live, with latency low enough that conversation still works normally.

Alongside the voice engine there is a soundboard for triggering clips from the keyboard, and a set of tools for building your own voices by chaining pitch, formant, modulation and reverb stages rather than picking from a fixed menu.

Licence note: the free tier is genuinely free but rotates a limited selection of voices. The full library, unlimited custom voices and the commercial-use rights come with Voicemod Pro, which is paid. Download and account creation happen on Voicemod's own site.