Download
Currently the Geppetto Studio app is only available as installable Desktop application for Mac, Linux and Windows. In the future I hope to also make it available directly from the browser.
Installation
The apps are untrusted at the moment, if you don't trust it, you can either checkout the electron code at https://github.com/matthijsgroen/geppetto/tree/main/public/electron to review yourself if you trust what I'm doing.
Open an untrusted app on Mac
https://support.apple.com/guide/mac-help/open-a-mac-app-from-an-unidentified-developer-mh40616/mac