Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.
GnuPG - GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP).
File Lock PEA - Password-encryption of files and directories. File PEA encrypts files and folders with authenticated encryption to protect confidentiality and integrity. The program uses memory-hard key derivation functions to prevent custom hardware attacks.
Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
Axcrypt - AxCrypt - Password Protect Files With Strong Encryption. AxCrypt is the leading open source file encryption software for Windows.
PGP Tool - PGPTool allows you to encrypt and decrypt files. It's free and easy to use.