Gpg4win (GNU Privacy Guard for Windows) is encryption software for files and emails.
It 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 came from a specific sender.
Gpg4win supports both relevant cryptography standards, OpenPGP and S/MIME (X.509), and is the official GnuPG distribution for Windows. The developers of GnuPG maintain it.
Linux users will need to compile from the source code available here.