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
VeraCrypt is a more advanced and actively developed successor to TrueCrypt, offering enhanced security features such as support for hidden volumes and modern encryption algorithms. In contrast, TrueCrypt, while easier to use, is no longer maintained and may pose security risks due to its outdated status.