OpenPGP is the most widely used email encryption standard in the world. It is defined by the OpenPGP Working Group of the Internet Engineering Task Force (IETF) Proposed Standard RFC4880. The OpenPGP standard was originally derived from PGP (Pretty Good Privacy), first created by Phil Zimmermann in 1991.
OpenPGP Encrypt & Decrypt:
The OpenPGP Card is a specification of an ISO 7816-4,-8 compatible smartcard and also an actually available implementation of this specification as a standard sized card.
GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP). GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications. A wealth of frontend applications and libraries are available. Version 2 of GnuPG also provides support for S/MIME and Secure Shell (ssh).
Download GnuPG: https://gnupg.org/download/index.html
On macOS, you can install GPG Suite: https://gpgtools.org/