GnuPG, commonly known as GPG, is a comprehensive, free solution for data encryption and signature, compliant with the OpenPGP standard (RFC4880). It's designed for encrypting and signing data and communications, offering a robust key management system and support for various public key directories. Notable for its command-line tool, GnuPG also integrates seamlessly with other applications and supports frontends and libraries, S/MIME, and Secure Shell (ssh). It's a cornerstone tool for privacy, utilized even by privacy advocates like Edward Snowden. GnuPG is Free Software, available under the GNU General Public License, ensuring it can be freely used, modified, and distributed.