Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
YAATA - YAATA app offers features that let you send multimedia files such as images, videos, audio, and GIFs, etc.
Tutanota - Get your encrypted mailbox for free.
Ciphermail for Android - CipherMail for Android is an Android application which can be used with your existing Android mail...
Mailvelope - Mailvelope open source project. OpenPGP in your browser.