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.
fstransform is a tool to change a file-system from one format to another. For example, it can change from jfs, xfs, or reiser to ext2, ext3, or ext4. It works in-place and without the need for backup. It currently has been tested on Linux only. It uses a sparse file to create the new file-system image, moves all the files of the existing file-system into it, then remaps the sparse file to the original partition.