APG!

GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications. A wealth of frontend applications and libraries are available. Version 2 of GnuPG also provides support for S/MIME.

Enigmail is a security extension to Mozilla Thunderbird and SeaMonkey. It enables you to write and receive email messages signed and/or encrypted with the OpenPGP standard.

OpenKeychain helps you communicate more privately and securely. It uses high-quality modern encryption to ensure that your messages can be read only by the people you send them to, others can send you messages that only you can read, and these messages can be digitally signed so the people getting them are sure who sent them. OpenKeychain is based on the well established OpenPGP standard making encryption compatible across your devices and operating systems.

GPG for Mailis an open source plugin for Apple Mail. Encrypt, decrypt, sign and verify mails using OpenPGP with a few simple clicks.

GPGMail is an open source plugin for Apple Mail. It brings the functionality to sign, verify, encrypt and decrypt mails using the OpenPGP standard.

WebPG is a free, open source suite of tools to bring GnuPG/PGP (gpg, gnupg) to the browser, in an effort to make cryptographic methods usable, safe and accessible to the common man.WebPG encompasses several projects, from the backend technology that interfaces with GnuPG/PGP (gpg, gnupg), to the user interface utilities that bring those methods to the browser.

iPGMail is an app that implements the OpenPGP standard (RFC 4880, RFC 6637) and allows the user to create and manage both public and private (RSA, DSA, ECDSA) PGP keys and send and receive PGP encrypted messages.

S/MIME email encryption and digital signatures for Android devices

OneTime is an open source encryption program that uses the one-time pad algorithm to allow two parties to communicate privately. It has features to assist with the bureaucracy of pad management, and comes with built-in help. OneTime requires Python 2.6 or higher, and is for users who are comfortable running command-line programs.

oPenGP is a solution to support OpenPGP standard (RFC 4880) on your iOS device.