Awesome Privacy

Application for managing encryption keys and passwords, integrated with the GNOME Keyring.

Certificate manager and a universal crypto GUI. It supports managing X.509 and OpenPGP certificates in the GpgSM keybox and retrieving certificates from LDAP servers.

Kleopatra ported to Windows.

Successor of MacGPG. Plays nice with MacOS apps, including Finder, Appple Mail, Keychain and Spotlight. Makes encrypting files, emails, and messages / data very easy. As well as GUI for generating keys, verifying signatures, etc.

Android app for managing keys, and encrypting messages. Works both stand-alone, and as integrated into other apps, including k9-Mail. Everything can be done through a simple yet powerful GUI. Open source, security audited, transparent permissions, and activley maintained.

iOS app for encrypting/ decrypting text. Has native keyboard integration, keychain support and app integrations which makes it quick to use in any app.

Browser extension for using PGP within Gmail, for Chrome and Firefox. Mobile version supported on Android and iOS.

OpenPGP extension for Thunderbird and PostBox, integrates natively within mail app.

Mailvelope is an addon for email applications, that makes using PGP very easy for beginners. You can use the hosted version for free, or opt to host your own instance. Works with Gmail, Yahoo, Outlook, GMX, Posteo, Web.de, FreeNet.de, Mailbox.org and many others.