ProxyCrypt is a command line tool that creates encrypted volumes within a file or a hard drive. Designed for paranoids and advanced users, it is also fast, very lightweight, open source and easy to recompile. It works as a 'proxy' for the ImDisk driver, which is included in the full package. If you need to create encrypted spaces which can be partitioned like an ordinary hard drive, it is also compatible with Arsenal Image Mounter.