TrueCrypt is an open source software to encrypt volumes of data. It even supports the creation of virtual encrypted volumes which is portable. Developed by TrueCrypt Foundation
License: Open Source
TrueCrypt is a powerful but outdated disk encryption tool that offers a wide range of features including hidden volumes and cross-platform support, while FreeOTFE is a portable alternative that focuses on simplicity and ease of use. However, TrueCrypt's lack of updates raises security concerns, making FreeOTFE a more viable option for users seeking a modern solution.