CrossBox is described as 'Real-time email, chat, audio/video calls & conferences, file-sharing, and contacts app with a modern and intuitive UI' and is a Mail Server in the Office & Productivity category. There are more than 25 alternatives to CrossBox for a variety of platforms, including Linux, Online / Web-based, Windows, Self-Hosted solutions and Mac. Most alternatives are Mail Servers and WebMail Providers. The best alternative is Roundcube, which is both free and Open Source. Other great apps like CrossBox are Zoho (Paid), Google Workspace (Paid), mailcow: dockerized (Free, Open Source) and Microsoft 365 (Paid).
Roundcube webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an e-mail client, including MIME support, address book, folder manipulation, message searching and spell checking.
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.
Horde Groupware is a free, enterprise ready, browser based collaboration suite. Users can manage and share calendars, contacts, tasks and notes with the standards compliant components from the Horde Project.
Nextcloud is the most deployed on-premises file share and collaboration platform. Access & collaborate across your devices. As fully on-premises solution, Nextcloud Hub provides the benefits of online collaboration without the compliance and security risks.