Corvette
This is a prototype for a successor of the Thunderbird email client. It is a desktop email client written entirely in JavaScript and HTML. It should later run on smartphones as app as well, using a different UI.
It is currently based on Electron as runtime, but may be adapted to use other runtimes like XULRunner and Cordova as well.
It makes an emphasis on clean code architecture and design and APIs, to allow easy modification and adaptions to new needs. It will also support extensions, which should be easier to write than XUL extensions for Thunderbird, thanks to the easier API.
The target user group is primarily the Thunderbird users, but also all those people who use webmail or the standard system email app today.
For now, this is just a modest prototype.