TrueCrypt 5.0

TrueCrypt - Free Open-Source Disk Encryption Software

Main Features:

Creates a virtual encrypted disk within a file and mounts it as a real disk.
Encrypts an entire hard disk partition or a storage device such as USB flash drive.
Encryption is automatic, real-time (on-the-fly) and transparent.
Provides two levels of plausible deniability, in case an adversary forces you to reveal the password:

1) Hidden volume (steganography – more information may be found here).

2) No TrueCrypt volume can be identified (volumes cannot be distinguished from random data).
Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.
Further information regarding features of the software may be found in the documentation.