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 https://www.gnupg.org/related_software/frontends.html & https://www.gnupg.org/related_software/libraries.html are available. Version 2 of GnuPG also provides support for S/MIME and Secure Shell (ssh).
GnuPG is http://www.gnu.org/philosophy/free-sw.html (meaning that it respects your freedom). It can be freely used, modified and distributed under the terms of the http://www.gnu.org/copyleft/gpl.html
GnuPG comes in two flavours: 1.4.18 is the well known and portable standalone version, whereas 2.0.26 is the enhanced and modern version and suggested for most users.
Project http://www.gpg4win.org/ provides a Windows version of GnuPG. It is nicely integrated into an installer and features several frontends as well as English and German manuals.
Project GPGTools provides a Mac OS X version of GnuPG. It is nicely integrated into an installer and features all required tools. https://gpgtools.org/
