eSpeak-NG is an open source speech synthesis module, forked from open source eSpeak software. Please refer these projects to ensure its copyrights.
The iOS/macOS port was originated by Yury Popov (@djphoenix) in 2022.
The iOS/macOS port are separated to two modules.
The first (called Extension) is Audio Unit Application Extension, that links statically with libespeak-ng library. As espeak-ng licensed under GPLv3, Extension inherits it too. So all Extension code is licensed under GPLv3.
The second module (called Application) is an user-interface frontend. It does not linked with libespeak-ng nor Extension, and communicates with Audio Unit with XPC. So it does not inherits a GPLv3 license. For possible reuse its code with other synthesizing libraries, all Application code is licensed under MIT license
As both modules are contained in single Xcode project, xcodeproj and related files is licensed under GPLv3.