Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Microsoft 365 - Boost your productivity with reliable access anywhere with services like email, calendar, file sharing, meetings, instant messaging, and Office Online
Roundcube - Web-based IMAP email client
YouTeam - YouTeam is a new, smarter way to outsource.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.