ClearOS - A very good alternative for Windows Server, for free
Roundcube - Web-based IMAP email client
NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
FreeIPA - FreeIPA is an integrated security information management solution combining Linux (Fedora), 389...
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.