The Sleuth Kit
The Sleuth Kit (previously known as TASK) is a collection of UNIX-based command line file and volume system forensic analysis tools. The file system tools allow you to examine file systems of a suspect computer in a non-intrusive fashion. Because the tools do not rely on the operating system to process the file systems, deleted and hidden content is shown.
The volume system (media management) tools allow you to examine the layout of disks and other media. The Sleuth Kit supports DOS partitions, BSD partitions (disk labels), Mac partitions, Sun slices (Volume Table of Contents), and GPT disks. With these tools, you can identify where partitions are located and extract them so that they can be analyzed with file system analysis tools.
When performing a complete analysis of a system, we all know that command line tools can become tedious. The Autopsy Forensic Browser is a graphical interface to the tools in The Sleuth Kit, which allows you to more easily conduct an investigation. Autopsy provides case management, image integrity, keyword searching, and other automated operations.
More details about TSK can be found here.