Forensics

Steganography - Tasked with finding information hidden in files or images

Steghide — Hide data in various kind of images
Stegsolve — Apply various steganography techniques to images
Zsteg — PNG/BMP analysis
Exiftool — Read and write meta information in files
Pngtools — For various analysis related to PNGs

Forensics

Audacity — Analyze sound files (mp3, m4a, whatever)
Bkhive and Samdump2 — Dump SYSTEM and SAM files
CFF Explorer — PE Editor
Creddump — Dump windows credentials
Foremost — Extract particular kind of files using headers
NetworkMiner — Network Forensic Analysis Tool
Shellbags — Investigate NT_USER.dat files
UsbForensics — Contains many tools for USB forensics
Volatility — To investigate memory dumps