Squashfs is a highly compressed read-only filesystem for Linux. It uses zlib to compress files, inodes, and directories. All blocks are packed to minimize the data overhead, and block sizes of between 4K and 1M are supported. It is intended to be used for archival use, for live CDs, and for embedded systems where low overhead is needed.
autofs is a kernel-based automounter for Linux. It performs a job similar to amd but relies on a small stub of kernel code instead of pretending to be an NFS server. The result is simpler code, better reliability, and much faster operation in the common case (everything already mounted). Autofs 4 adds support for automounting trees of exported filesystems via /net.
DFF (Digital Forensics Framework) is a simple but powerful tool with a flexible module system which will help you in your digital forensics works, including file recovery due to error or crash, evidence research and analysis, etc. DFF provides a robust architecture and some handy modules.
Unison is a file-synchronization tool for Unix and Windows. It allows two copies of a collection of files and directories to be stored on different hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other. Unison can deal with updates to both replicas of a distributed directory structure. Updates that do not conflict are propagated automatically. Conflicting updates are detected and displayed. Unison can communicate through a direct socket link or through an rsh/ssh tunnel. It uses network bandwidth efficiently.
Plash is a sandbox for running GNU/Linux programs with minimum privileges. It is suitable for running both command line and GUI programs. It can dynamically grant Gtk-based GUI applications access rights to individual files that you want to open or edit. This happens transparently through the Open/Save file chooser dialog box, by replacing GtkFileChooserDialog. Plash virtualizes the file namespace and provides per-process/per-sandbox namespaces. It can grant processes read-only or read-write access to specific files and directories, mapped at any point in the filesystem namespace. It does not require modifications to the Linux kernel.
LUFS is a hybrid userspace filesystem framework supporting many "exotic" filesystems (localfs, sshfs, ftpfs, httpfs, socketfs, freenetfs, and nutellafs) transparently for any application. It can be regarded as doing the same job as the VFS (virtual filesystem switch) in the kernel: it is a switch, distributing the filesystem calls to its supported filesystems. However, LUFS filesystems are implemented in userspace. This would be a drawback for local filesystems where the access speed is important, but proves to be a huge advantage for networked filesystems where the userland flexibility is most important.
openMosix is a a set of extensions to the standard Linux kernel allowing you to build a cluster of out of off-the-shelf PC hardware. openMosix scales perfectly up to thousands of nodes. You do not need to modify your applications to benefit from your cluster (unlike PVM, MPI, Linda, etc.). Processes in openMosix migrate transparently between nodes and the cluster will always auto-balance.