Wikipedia
DiskCryptor is a full disk encryption system for Microsoft Windows that allows the encryption of an PC's entire hard drive or individual partitions – including the ability to encrypt the partition and disk on which the OS is installed.
DiskCryptor was originally designed to replace commercial disk encryption systems such as DriveCrypt Plus Pack and PGP Whole Disk Encryption, and uses either AES-256, Twofish, Serpent or a combination of cascaded algorithms in XTS mode to carry out encryption.
The project was originally started by a former TrueCrypt user and forum member who goes by the name of 'ntldr' (anonymous). It was originally fully compatible with TrueCrypt's container format but has since improved on the format in order to allow data-in-place encryption on Windows XP, to allow the system partition to have exactly the same format as non-system partitions and to support future project plans.