License

Spellophone is free software, released under the GNU General Public License, version 3 or later (GPL-3.0-or-later), the same license as espeak-ng.

That covers everything in the repository: the C glue, the TypeScript, the build scripts, the documentation and the examples. The compiled wasm/ and espeak-ng-data/ artifacts are built from espeak-ng's sources and carry espeak-ng's license.

What this means for your project

The GPL is a copyleft license. An application that links Spellophone, which includes bundling it into a web app or importing it in a Node.js program, is a derivative work and has to be released under the GPL as well, with its source available to its users. If that does not fit your project, Spellophone is not the right choice; there is no other license available, because espeak-ng itself is GPL.

espeak-ng

espeak-ng is copyright its authors, principally Jonathan Duddington (eSpeak) and Reece H. Dunn (eSpeak NG), and is distributed under the GPL version 3 or later. Its bundled ucd-tools is Apache-2.0 and its Unicode data is under the Unicode license; speechPlayer is GPL-3.0-or-later. See the COPYING* files in the espeak-ng repository.

The 2017 emscripten/ port that ships inside espeak-ng, by Eitan Isaacson and Alberto Pettarin, was the starting point for understanding how to build espeak-ng for the web. Spellophone's build and glue are a rewrite, not a copy.