TODO (Feel Free to add information, please indicate if it is Free Software or not and if it uses the recommended ~G~PGME and uiserver ~APIs of ~GnuPG)

=== Enigmail

https://www.enigmail.net

//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 ~G~PGME**, **no UIServer**

=== Mailpile

| https://www.mailpile.is | GNU AGPL & Apache 2 | their own (?) gpgi.py, **no** ~G~PGME, **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 ~G~PGME**, **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 ~G~P~GME. 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 ~G~PGME**

=== ~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 ~G~PGME**).

=== 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