Knox - Knox offers easy disk image encryption and comes with a built-in backup service.
GnuPG - GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP).
Kruptos - Lock and encrypt your photos, movies, files and folders using 256-bit file encryption.
Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
R-Crypto - R-Crypto is smart data security and disk encryption software that allows you to secure your sensitive information via strong encryption.
PGP Tool - PGPTool allows you to encrypt and decrypt files. It's free and easy to use.