VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
Jetico BCTextEncoder - Jetico BCTextEncoder is software that ensures your text-based communications are safe by allowing you to encrypt them.
Axcrypt - AxCrypt - Password Protect Files With Strong Encryption. AxCrypt is the leading open source file encryption software for Windows.
TheLetterEncrypter - TheLetterEncrypter is a small (14KB download) AES-based text-encryption program.
Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.
GNUPGK - A GnuPG Frontend GUI made in C#.