TOCC is a Tool for Obsessive Compulsive Classifiers. It implements a file system that uses tags instead of folders, allowing you to classify files however you want. For example, you could tag photos by location, people, and technique (e.g. black & white, HDR). Finding files is as simple as running a query like "give me all files tagged photo and my-love".
RecDB is a recommendation engine built entirely inside PostgreSQL 9.2. It allows application developers to build recommendation applications using a wide variety of built-in recommendation algorithms such as user-user collaborative filtering, item-item collaborative filtering, and singular value decomposition. Applications powered by RecDB can produce online and flexible personalized recommendations to end-users. It is easily used and configured and allows novice developers to define a variety of recommenders that fits their application's needs in few lines of SQL. It can seamlessly integrate recommendation functionality with traditional database operations.
Gpart is a small tool which tries to guess which partitions are on a PC harddisk in case the primary partition table was damaged. It works by scanning through the device (or file) given on the commandline on a sector basis. Each guessing module is asked if it thinks a filesystem it knows about could start at a given sector. Several filesystem guessing modules are built in, and others can be added dynamically.