aerc - Highly efficient and extensible email client for the terminal
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Netlify - Build, deploy and host your static site or app with a drag and drop interface and automatic delpoys from GitHub or Bitbucket
Geary - Geary is an email application built for GNOME 3.
Coolify - An open-source, hassle-free, self-hostable Heroku & Netlify alternative.
The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.