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.
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.
mailcow - An open source mailserver suite.
RingCentral Video - Live life unlimited. Free video meetings and team messaging in one app that works the way you do.
Mail-in-a-box - Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software and also includes contacts and calendar synchronization.