Citadel is described as 'Is a collaboration suite (messaging and groupware). It is designed to run on open source operating systems such as Linux or BSD. In order to modernize the Citadel platform for the Internet, the Citadel/UX developers added functionality such as shared calendars, instant' and is a webmail provider in the office & productivity category. There are more than 10 alternatives to Citadel for a variety of platforms, including Linux, Web-based, Windows, Self-Hosted and Mac apps. The best Citadel alternative is Kolab, which is both free and Open Source. Other great apps like Citadel are Zimbra Collaboration Suite, hMail Server, Microsoft Exchange and SmarterMail Mail Server.
Kolab provides a FOSS communication & collaboration solution that can be completely self-hosted. Take back control of your data and access it via the webinterface, or existing mobile & desktop clients.
Kolab is the most popular Web-based, Linux & Self-Hosted alternative to Citadel.
Kolab is the most popular Open Source & free alternative to Citadel.
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 commercial alternative to Citadel.
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.
Exchange business-class email helps increase user productivity while protecting your data. Get it as a hosted service or run it on your servers.
SmarterMail is the only other email server on the market with native support for MAPI, the protocol that powers Exchange and Outlook. That means anything you can do on Exchange you can do with SmarterMail: no plug-ins and no additional software required.
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.
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.
Web-based team collaboration suite combining email client, calendar, contact and task tools, CRM, project and file management, file sharing, trouble tickets, Rocket.Chat chat, and Collabora online editing. Offers open source, self-hosted, and SaaS options.
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.
Atmail webmail system offers a webmail client, email server platform and mailserver appliance for Linux, Unix and Windows.
Turnkey Solutions for the Enterprise Cloud
Installation, Configuration, and Management tools for enterprise email, collaboration, messaging, video conferencing, file sharing, and file transfers.
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