TODO (Feel Free to add information, please indicate if it is Free Software or not and if it uses the recommended GPGME and uiserver APIs of GnuPG)
Enigmail
a data encryption and decryption extension for Mozilla Thunderbird and the SeaMonkey internet suite that provides OpenPGP public key e-mail encryption and signing.
License: MPL 2, GNU GPL 2+
API: no GPGME, no UIServer
Mailpile
| https://www.mailpile.is | GNU AGPL & Apache 2 | their own (?) gpgi.py, no GPGME, no UIServer | EMail Client, experimental: Mailpile UI is written using HTML5 and Javascript, running against a self-hosted Python application |
CipherMail Email Encryption Gateway
http://www.ciphermail.com/gateway.html
License GNU +APL 3 (some additional permissions)
Former DJIGZO provides a solution to securing your email without requiring additional client software. The centralized policy based encryption engine can be setup to automatically encrypt email based on regulatory compliance or business rules
API: no GPGME, no UIServer. Seems to call gpg directly.
Schleuder, Crypto Mailinglistproduct
| http://schleuder2.nadir.org/ | GNU GPL 2 | TODO | Mailinglist with encryption |
gpg4usb
http://www.gpg4usb.org seems to use GnuPG 1.4.x and Qt.
portable-application, which combines a simple text-editor with a GnuPG-frontend to write, encrypt and decrypt your text-messages and files.
API: Version 0.3.3 may still use GPGME. The TODO file aims for the use of its own kgpg connection. no UIServer
duplicity
Duplicity backs directories by producing encrypted tar-format volumes and uploading them to a remote or local file server. [..] uses GnuPG to encrypt and/or sign these archives
License GNU GPL v>=2.
API: uses its own embedded gpginterface.py, process based, does not use GPGME
~GoodCrypto
GoodCrypto offers an open source live operating system at https://goodcrypto.com which automatically encrypts and decrypts mail for everyone in a group. The server software runs on your system and integrates GPG into your MTA. GoodCrypto publishes the libraries source at https://gibhub.com/goodcrypto/. Libraries are licensed under GNU GPLv3. The rest of the source is in the ISO. License details are at https://goodcrypto.com/qna/technical/goodcrypto-open-source/. API: GoodCrypto calls GnuPG directly (does not use GPGME).
Confidant Mail
Confidant Mail is an email client and server using GPG encryption and signatures. It is not based on SMTP, but uses a block-oriented protocol which allows unlimited attachment length. It supports Tor and I2P anonymity, and has its own key distribution system. Works with GnuPG 1.4.19 or 2.1.1, does not use GPGME, uses gnupg.py and direct calls to GPG. Windows, Linux, MacOS. GNU GPL. https://www.confidantmail.org