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
CipherShed is a fork of TrueCrypt that aims to enhance security and user experience, while TrueCrypt, despite its popularity, is no longer maintained. Both offer strong encryption and cross-platform support, but CipherShed offers a more modern approach with additional features.