gpg4usb!

Gpg4win is an installer package for Windows (2000/XP/2003/Vista) with computer programs and handbooks for email and file encryption. Both relevant cryptography standards are supported, OpenPGP and S/MIME. Gpg4win and the software included with Gpg4win are Free Software (among other things free of charge for all commercial and non-commercial purposes).

GPGTools is an open source initiative to bring OpenPGP to Apple OS X in the form of an easy installer package. This allows you to sign, verify, encrypt, and decrypt files and e-mails. Read the introduction to get a detailed idea of how PGP works.

GPGshell is a Windows GUI for the GNU Privacy Guard - an open source software suite for public-key cryptography compatible with PGP. It provides a simple-ish interface to manage the encryption keys, encrypt and sign files, check the signatures and the like. It is freeware (though, unlike GPG, not free software) and with little effort can be made portable.

A GnuPG Frontend GUI made in C#. It is compatible with PGP as well so it can be a very useful tool for encryption/decryption. It also incorporates a shell extension so it can be easy to right click and decrypt or decrypt.

Simple portable GUI for GnuPG that lets you encrypt & decrypt data.