Free open-source disk encryption, provides transparently encrypted disk images, partitions, and entire storage device encryption.

Users can use TrueCrypt to create plausible deniability by using what are called hidden volumes. One password will decrypt and allow access to one volume while a different password will reveal an entirely different set of encrypted files, with no way to discover the existence of both.

TrueCrypt is fast! Data is read and written in parallel and with hardware acceleration, making access to encrypted data just as fast as regular. Multiple encryption algorithms are supported, and they can be combined in a cascade for maximum cryptographic security.