Google Workspace delivers a cloud-based suite combining Gmail, Calendar, Meet & Drive to enhance collaboration through tools like Docs and Sheets. Offers secure storage options, custom domain emails, and robust management capabilities with 2FA and 24/7 support.

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.

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.

Axigen provides a multi-tenant, fully integrated, multi-platform, all-in-one email, calendaring and collaboration messaging solution. It grants extensive branding options and is localized in over 29 languages (including right-to-left writing mode).

Exchange business-class email helps increase user productivity while protecting your data. Get it as a hosted service or run it on your servers.

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.

OpenChange aims to provide a portable Open Source implementation of Microsoft Exchange Server and Exchange protocols.

Real-time email, chat, audio/video calls & conferences, file-sharing, and contacts app with a modern and intuitive UI.

IceWarp integrates all communication & collaboration features in one unified solution. Available in cloud or for on-premises deployment, IceWarp is a great tool to share and exchange all information and ideas online, offline or via mobile devices.

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.

Kerio Connect makes email, calendars, contacts and task management easy and affordable. With Kerio Connect, you have immediate, secure access to your communications anytime, anywhere, on any device - without complexity or expensive overhead.

Open Source Collaboration, providing integration with your existing Linux mailserver, native mobile phone support, Outlook "Look & Feel" webaccess and stable Outlook sharing (100% MAPI).