pump.io : Social server with an ActivityStreams API. It's a stream server that does most of what people really want from a social network.
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...
Cool QL Cool : CoolQLCool (CQC) is an open source GraphQL server that allows you to turn websites into GraphQL APIs.
Appwrite : Appwrite is an end-to-end backend server for Web, Mobile, Native, or Backend apps packaged as a set of Docker microservices. Appwrite abstracts the co...
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.