How we built a Linux desktop app with Electron: 
Tutanota is a secure, open source email service that’s been available as an app for the browser, iOS, and Android. The client code is published under GPLv3 and the Android app is available on F-Droid to enable everyone to use a completely Google-free version.
read more: Opensource.com Nils Ganther
Supporting Open Source.
Have you tried: Diving with Sharks?