Roundcube is described as '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' and is a very popular webmail provider in the office & productivity category. There are more than 25 alternatives to Roundcube for a variety of platforms, including Self-Hosted, Web-based, Linux, PHP and Cloudron apps. The best Roundcube alternative is Rainloop, which is both free and Open Source. Other great apps like Roundcube are Mailpile, Kolab, SOGo and Zimbra Collaboration Suite.
NeoMail is a web-based mail client that allows users to access their mail spools and send messages. It does not require a POP3 server, or any shell access for the users. It interfaces directly with user mail spools.
High security web-based e-mail system which extends considerably the email system to much more than currently exists.
TrulyMail is an email client and a private messaging system, very feature rich (voice recording, script blocking, etc.).
United States