Keynesis Lockngo is a security application that runs directly from a portable drive. Lockngo encrypts and password-protects data against loss or theft. When protected, the drive appears empty (data is hidden) and will not allow new data to be written onto it. Lockngo has Military Grade 256-bit AES Encryption, FIPS 140-2 Certified. Lockngo also comes in a cross-platform version for Mac and Windows. This version allows you to lock a drive on a Macintosh and open it on a computer running Windows and vice versa.
fsprotect is a set of scripts that combine tmpfs and aufs to make existing filesystems immutable. After the filesystems are protected, everything that is written will be lost when the computer powers off. It is a great tool for testing and for public computers like those in schools, libraries, etc. It is also very easy to use. It is currently available only for Debian-based systems.