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**).