Implementations different from GnuPG that aim for OpenPGP compliance.

OpenPGP.js

http://openpgpjs.org/

License: GNU LGPL v>=2.1.

used by:

• https://www.mailvelope.com/ (License GNU Affero v==3) for Webmail -- extensions for Chrome/Chromium & Firefox
• Mymail-Crypt for Gmail (License: GNU GPL v>=2) -- extension for Chrome/Chromium

Completeness: ?

Compatibility: ?

PGPy

https://github.com/SecurityInnovation/PGPy/ based on https://pypi.python.org/pypi/cryptography which is based on OpenSSL

kbpgp

https://github.com/keybase/kbpgp

Keybase's PGP for JS claims: Public-key crypto and improvements to OpenPGP.js

NetPGP

http://www.netpgp.com/

The latest versions offered on the website are from February 2014 and 2015 (last checked 2018-01-04).

golang.org/x/crypto/openpgp

https://godoc.org/golang.org/x/crypto/openpgp

NeoPG

https://neopg.io/

From the website: NeoPG starts as an opiniated fork of GnuPG 2 to clean up the code and make it easier to develop.

Sequoia PGP

• https://sequoia-pgp.org/
• https://gitlab.com/sequoia-pgp/sequoia

From the websites (2018-05-31):

Sequoia is a cool new OpenPGP implementation. It consists of several crates, providing both a low-level and a high-level API for dealing with OpenPGP data.

Our work is made possible by the p≡p foundation.

Chromium Extension End-to-End

https://code.google.com/p/end-to-end/

Completeness: ? Claims to only create ECC certificates (which curve parameters?)

Compatibility: ?

• Google announced a Chromium extension that supports OpenPGP, see http://googleonlinesecurity.blogspot.de/2014/06/making-end-to-end-encryption-easier-to.html
• Heise newsarticle in DE: http://www.heise.de/newsticker/meldung/Google-experimentiert-mit-End-to-End-Verschluesselung-fuer-GMail-2215680.html

Android Privacy Guard

http://thialfihar.org/projects/apg/

Completeness: ?

Compatibility: ?

Integrates with the K-9 Mailer.

Seems to be unmaintained (last release 2014-03, some known vulnerabilities unfixed since (status 2016-04)) with OpenKeychain being the activeley maintained "fork", see ~OpenKeychain FAQ: relation to APG

OpenPGP-Keychain

https://www.openkeychain.org/, started as a continuation of APG. Uses a repackaged Bouncy Castle: https://rtyley.github.io/spongycastle/

Completeness: ?

Compatibility: ?

Integrates with the K-9 Mailer.

Bouncy Castle

https://en.wikipedia.org/wiki/Bouncy_Castle_(cryptography) (Homepage with ads: https://bouncycastle.org/)

Completeness: ?

Compatibility: ?

hOpenPGP

http://hackage.haskell.org/package/hOpenPGP

native Haskell implementation of OpenPGP (RFC4880), plus Camellia (RFC5581)

Discussion

• https://news.ycombinator.com/item?id=7843297 Discussion about OpenPGP.js codequality and choice of reimplementation in End-to-End.
• [2] https://lwn.net/Articles/742542/ (subscriber contents to become generally available 10th of January, 2018) Future directions for PGP, January 3, 2018 by J. B. Crawford, lists NetPGP and NeoPGP.