Editor: OSXCrypt is a framework, a kernel extension and a command line utility that allows the creation, manipulation and attaching of a TrueCrypt -compatible volume, and in the near future, any kind of disk-based encryption available through a modular architecture.
Some of the differences between TrueCrypt and OSXCrypt are:
OSXCrypt is a kernel module, and not based on MacFUSE. That gives the project a really different approach.
The OSXCrypt Framework is based on the paradigm of implementing a modular kernel module that can be used with OTHER cyphers. Implementing dm-cryppt on mac, for example, is now trivially easy.
The GUI is coming even here, thanks to the efforts of a volunteer.
Source Code can be found here - http://www.osxcrypt.org/release/OSXCrypt-6.2A-source.zip