Free and simple TrueCrypt Implementation based on dm-crypt
tcplay is a free (BSD-licensed), pretty much fully featured (including multiple keyfiles, cipher cascades, etc) and stable TrueCrypt implementation.
This implementation supports mapping (opening) both system and normal TrueCrypt volumes, as well as opening hidden volumes and opening an outer volume while protecting a hidden volume. There is also support to create volumes, including hidden volumes, etc. Since version 1.1, there is also support for restoring from the backup header (if present), change passphrase, keyfile and PBKDF2 PRF function.