Gpg4win enables users to securely transport emails and files with the help of encryption and digital signatures. Encryption protects the contents against an unwanted party reading it. Digital signatures make sure that it was not modified and comes from a specific sender. Gpg4win supports both relevant cryptography standards, OpenPGP and S/MIME (X.509), and is the official GnuPG distribution for Windows. It is maintained by the developers of GnuPG. Gpg4win and the software included with Gpg4win are Free Software (Open Source; among other things free of charge for all commercial and non-commercial purposes).
Gpg4win is an installer for Windows and contains several Free Software components:
GnuPG: The core; this is the actual encryption tool.
Kleopatra: A certificate manager for OpenPGP and X.509 (S/MIME) and common crypto dialogs.
GPA: An alternative certificate manager for OpenPGP and X.509 (S/MIME).
GpgOL: A plugin for Microsoft Outlook 2003 and 2007 (email encryption).
GpgEX: A plugin for Microsoft Explorer 32bit (file encryption).
Claws Mail: A complete email application with crypto support.
Gpg4win Compendium: The documentation (for beginner and advanced users), available in English and German.