Riot : Riot allows teams to communicate across a wide range of collaboration apps. If some team members use Riot while others use IRC, Slack or Gitter, Riot ...
SimpleLogin : With email aliases , you can be anonymous online and protect your inbox against spams and phishing. Open-source.
Mail-in-a-Box : Each Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software. It also includes contacts and calen...
WireMock : Free and Open Source tool for building mock APIs. Create stable development environments, isolate yourself from flakey 3rd parties and simulate APIs t...
Mailtrain : Mailtrain is a self hosted newsletter application built on Node.js (v5+) and MySQL (v5.5+ or MariaDB). Mailtrain supports subscriber list management, ...
Postal is a complete and fully featured mail server for use by websites & web servers. Think Sendgrid, Mailgun or Postmark but open source and ready for you to run on your own servers.