TrueCrypt

TrueCrypt is a software application used for on-the-fly encryption (OTFE). It is distributed without cost and the source code is available. It can create a virtual encrypted disk within a file or encrypt a partition or the entire storage device.

License: TrueCrypt License
Written in: C++,C,Assembly
Operating system: Cross-platform

Website: http://www.truecrypt.org/
Download: http://www.truecrypt.org/downloads
Documents: http://www.truecrypt.org/docs/