Not sure if I understood it correctly, but in essence it lets your users enter some (secret) content which is then encrypted in the browser using PGP.

Except for the message signing and auto-emailing, I've implemented something similar:

Blogpost: https://0day.work/easy-pgp-composer-encrypting-pgp-messages-...

GitHub: https://github.com/gehaxelt/PHP-Easy-PGP-Composer

Demo: http://pgpcomposer.demo.0day.work/