Project information: Cesium is wallet client software for Duniter crypto-currency, like Ğ1. Cesium allow you to manage your wallet, certify your friends, and more!
Cesium is an Unhosted Progressive Web Application (PWA), using AngularJS and Ionic
Homepage: Cesium Ğ1 - Site officiel
source code: GitHub - duniter/cesium: Webapp and Smartphone client for Duniter network
License: GNU AFFERO GENERAL PUBLIC LICENSE
Upstream has been contacted: There’s a request in the duniter forum Flatpak pour Cesium - Cesium - Duniter Forum, I think all the community will agree do a flatpak version of the cesium app.
I am not sure have enough knowledege to build a flatpak, but I am sure few developers from the community should join the project if so.