GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP). GnuPG allows you to encrypt and sign your data and communications; it features a versatile key management system, along with 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. GnuPG also provides support for S/MIME and Secure Shell (ssh).
Gnupg-pkcs1-scd is a project to implement a BSD-licensed smart-card daemon to enable the use of PKCS#11 tokens with GnuPG.