Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
Mailu - Mailu is a simple yet full-featured mail server as a set of Docker images.
Creativity 365 - Cross-device content creation suite
mailcow - An open source mailserver suite.
Microsoft Teams - Microsoft Teams provides the enterprise-level security, compliance and management features you expect from Office 365, including broad support for compliance standards, and eDiscovery and legal hold for channels, chats, and files.
Eudora Internet Mail Server - Eudora Internet Mail Server is a highly advanced internet mail system that supports the all kind of email systems and clients either it is IMAP, POP3, SMTP and much more.