Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more. With the most innovative web application available today, Zimbra boosts the productivity of users on any desktop and dramatically reduces TCO compared to legacy platform vendors.
- - Zimbra Collaboration Suite is the most popular Web-based, Linux & Self-Hosted alternative to Citadel.
- - Zimbra Collaboration Suite is the most popular Open Source & free alternative to Citadel.
Kolab is entirely Free and Open Source Software (a.k.a. FOSS), and uses Open Standards. We’ll get to why this is important to us, and hope that it is important to you thereafter.
Kolab Community Features
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 world.
- - hMail Server is the most popular Windows alternative to Citadel.
hMail Server is no longer supported by the people who created it and has been discontinued – so use it at your own risk.
The OX App Suite by Open-Xchange is web-based platform offering a suite of apps like an email client, calendar, contacts magement, cloud storage with synchronization and productivity apps for word processing, spreadsheets and presentations.
- - OX App Suite is the most popular SaaS alternative to Citadel.
OX App Suite Features
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 widely used by enterprises using Microsoft infrastructure solutions.
- - Microsoft Exchange Server is the most popular commercial alternative to Citadel.
Microsoft Exchange Server Features
Real-time email, chat, audio/video calls & conferences, file-sharing, and contacts app with a modern and intuitive UI.
- - CrossBox is the most popular Android, iPhone, iPad & Android Tablet alternative to Citadel.
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 sharing, Drop Box integration, client and server side encryption.
Online Collaboration with Chat and Online Office. Is developed as open source software in Germany, offered as free community version and as commercial version. Operation as self-hosted or as SaaS from the computer centre.
Open Source Collaboration, providing integration with your existing Linux mailserver, native mobile phone support, Outlook "Look & Feel" webaccess and stable Outlook sharing (100% MAPI).
- - Zarafa is the most popular Mac alternative to Citadel.
"Last year we released the announcement that Zarafa customers could transition to Kopano. We also announced that Zarafa would not be maintained beyond May 1st, 2017. Most ZCP customers have moved to a Kopano subscription now."
Atmail webmail system offers a webmail client, email server platform and mailserver appliance for Linux, Unix and Windows.
Atmail Email Server Features
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 mail accounts, storage, attachment size, custom logo. Free for commercial use.
Turnkey Solutions for the Enterprise Cloud
Installation, Configuration, and Management tools for enterprise email, collaboration, messaging, video conferencing, file sharing, and file transfers.
Expanding Communication Features