RoundCube
...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, spell checking and lots more ...
RainLoop - Simple, Modern & Fast Email Client.
...was designed with efficient memory use in mind. Regardless of mailbox size and number of mails in it, memory use per active user is always kept at a minimum, even when very large mails are processed and lots more great features...
