This top epic is holding stories that covers the creation of apps for Roundcube-Next:

Provided apps:

• Mandatory components that provide basic functionality but are not hard-wired into the shell and therefore are easily exchangeable.
• configuration (providing user settings and system config options)
• notifications (display all sorts of user notifications in an appropriate way and place)
• attachments (provide UI components for attachment upload)
• Mail app
• Contacts app