Apollo Solution

Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux.

Encrypt in real time, even as you add files. A wizard assists in creation of virtual encrypted volume (you define the size).

Main Features:

Creates a virtual encrypted disk within a file and mounts it as a real disk.

Encrypts an entire partition or storage device such as USB flash drive or hard drive.

Encrypts a partition or drive where Windows is installed (pre-boot authentication).

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.

Get it at http://www.truecrypt.org/