Roundcube
last commit 39 minutes ago, GNU GPLv3
The Roundcube Webmail suite
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183 commits past year
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Cypht
last commit 2 days ago, GNU LGPLv2.1
Cypht: Lightweight Open Source webmail written in PHP and JavaScript
858
232 commits past year
IMP
HORDE application that provides webmail access to IMAP and POP3 accounts.
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Open source disposable email address service.
SnappyMail
Simple, modern, lightweight & fast web-based email client
SquirrelMail
Another browser-based IMAP client.