Tutanota is an open-source end-to-end encrypted email software and freemium hosted secure email service.

The Bat! is an email program for Windows that protects the correspondence and empowers the users to handle large amounts of emails quickly and efficiently.

Gpg4win is an email and file encryption package for most versions of Microsoft Windows, which uses GnuPG public-key cryptography for data encryption.

Seahorse is a GNOME application for managing encryption keys and passwords in the GnomeKeyring.

GPGMail is an extension for Apple Mail that provides public key email encryption and signing.

K-9 Mail is an open source email client with support for multiple accounts, search, IMAP push email, multi-folder sync, flagging, filing, signatures.

Gajim is an instant messaging client for the XMPP protocol which uses the GTK+ toolkit.

Conversations is an open source XMPP/Jabber client for the Android platform.

MailMate is an IMAP email client for macOS featuring extensive keyboard control, Markdown integrated email composition, advanced search conditions.