Nylas Mail
An extensible desktop mail app built on the modern web
...Each folder in /packages is designed to be its own stand-alone repository. They are all bundled here for the ease of source control management. In early 2016, the Nylas Mail team wrote extensive documentation for the app that was intended for plugin developers. This documentation lives on GitHub Pages and offers a great overview of the app's architecture and important classes. When you download and build Nylas Mail from the source it runs without its cloud components. The concept of a "Nylas ID" / subscription has been removed, and plugins that require server-side processing are disabled by default. ...