Horde vs Round Cube Webmail
Horde Groupware Webmail
...is a free, enterprise ready, browser based communication suite. Users can read, send and organize email messages and manage and share calendars, contacts, tasks, notes, files, and bookmarks with the standards compliant components from the Horde Project.
...is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an email client, including MIME support, address book, folder manipulation, message searching and spell checking.