File Encryption XP - A program designed for protecting confidential information stored on your computer.
GnuPG - GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP).
S.S.E. File Encryptor - S.S.E. File Encryptor is a cross-platform encrypter/decrypter of files and folders.
Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
CrococryptFile - Strong file encryption tool
PGP Tool - PGPTool allows you to encrypt and decrypt files. It's free and easy to use.