Alternatives to Citadel for all platforms with any license

Kolab Community

Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.

Free Open Source Linux Web Self-Hosted
CalDAV CardDAV Real time collaboration Support for WebDAV Add a feature

36 Like
Zimbra Collaboration Suite

Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more. With the most innovative web application available today, Zimbra...

Freemium Linux Web
ActiveSync Real time collaboration Add a feature

28 Like
hMail Server

hMailServer is a free e-mail server for Microsoft Windows. Its used by Internet service providers, companies, governments, schools and enthusiasts in all parts of the...

Free Open Source Windows
POP3 Support Add a feature

21 Like
OX Open-Xchange

Open-Xchange Server 6 is the most advanced Linux based Groupware solution f. Open-Xchange Server 6 is superior in the following areas: • Open-Xchange Server 6 offers...

Free Open Source Linux Web
Real time collaboration Support for WebDAV Add a feature

11 Like
Microsoft Exchange Server

Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft. It is part of the Microsoft Servers line of server products and is...

Commercial Windows Web
Real time collaboration Add a feature

15 Like
Zarafa

Open Source Collaboration, providing integration with your existing Linux mailserver, native mobile phone support, Outlook "Look & Feel" webaccess and...

Commercial Mac OS X Windows Linux Web
Real time collaboration Add a feature

13 Like
MDaemon Messaging Server

Low cost, easy to use Email Server software for virtual, on-premise, or hosted deployments for companies that want control of their email. Integrated web-mail with doc...

Commercial Windows
Dropbox integration Encrypted email Group chat Support for IMAP ... Outlook integration Add a feature

14 Like
Atmail Email Server

Atmail webmail system offers a webmail client, email server platform and mailserver appliance for Linux, Unix and Windows. Features: Webmail Calendar Addressbook ...

Commercial Linux Web
File-sync Group Mail Add a feature

7 Like
iMail

Fast, safe, heavy mail solution. Web-client access, LAN or WAN self-hosted server, maintenance-free design. No Windows server and database server required, unlimited...

Free Windows Self-Hosted
No features added Add a feature

2 Like
eGroupWare

Egroupware is a web based software for team collaboration, central data management and CRM: email client, online calendar, contact and task management, project and file...

Free Open Source Linux Web
No features added Add a feature

7 Like
Expanding Communication

Turnkey Solutions for the Enterprise Cloud Installation, Configuration, and Management tools for enterprise email, collaboration, messaging, video conferencing, file...

Commercial Linux
CalDAV Add a feature

5 Like
SophiMail

SophiMail is a fully-featured email and collaboration server solving the most critical email issues: maximizes Privacy, Portability and Cost efficiency, Admin & User...

Free BSD VirtualBox Self-Hosted VMware vSphere Hypervisor
Daily Backup Indexed search CalDAV CardDAV ... Data portability Privacy focused Private messaging Schedule Backup Security focused Selective folder sharing Shared folders Team Collaboration Two factor authentication Unlimited users Add a feature

6 Like
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Xeams

Xeams is a secure and powerful mail server for that includes a powerful spam filtering engine that eliminates up to 99% of junk email right out of the box. The software...

Free Personal $ $ $ Mac Windows Linux BSD
No features added Add a feature

1 Like
Netrepid Hosted Exchange Services

Hosted Exchange solutions from Netrepid - the best hosted exchange provider. Accelerate your technology at on demand speed.

Commercial Web
No features added Add a feature

1 Like
SmarterMail Mail Server

SmarterMail delivers Exchange-level email server software features for a fraction of the cost. With lower hardware requirements, superior stability and reduced...

Freemium Windows
No features added Add a feature

2 Like