TrueCrypt – Free Open Source On the Fly Disk Encryption Software
http://www.truecrypt.org/

Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux Main featiures include: 1) Creates a virtual encrypted disk within a file and mounts it as a real disk; 2) Encrypts an entire partition or storage device such as USB flash drive or hard drive; 3) Encrypts a partition or drive where Windows is installed (pre-boot authentication); 4) Encryption is automatic, real-time (on-the-fly) and transparent; 5) Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted; 6) Provides plausible deniability, in case an adversary forces you to reveal the password: Hidden volume (steganography) and hidden operating system; and 7) Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS. Further information regarding features of the software may be found in the documentation. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog. This has been added to Privacy Resources Subject Tracer™ Information Blog.