Knox - Knox offers easy disk image encryption and comes with a built-in backup service.
VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
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.
Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.