SOGo is a free and modern scalable groupware server. It offers shared calendars, address books, and emails through your favourite Web browser and by using a native client such as Mozilla Thunderbird and Lightning.

SOGo is standard-compliant. It supports CalDAV, CardDAV, GroupDAV, iMIP and iTIP and reuses existing IMAP, SMTP and database servers - making the solution easy to deploy and interoperable with many applications.

ALT Linux Wiki: https://www.altlinux.org/SOGo

Home page: https://www.sogo.nu/