Network/Security


NMAP - Network exploration and auditing
Wireshark - Network Protocol Analyzer
SNORT - IDS (intrusion Detection System)
NetCat - R/W Data across network connections
OpenSSH - Free SSH connectivity tools
Putty - Windows ssh/COM/telnet client utilities
AirCrack - 802.11 WEP/WPA key recovery tool
ttcp - Test TCP traffic generator
tcpproxy - Simple tcp proxy server

FileSystem Test and Benchmark


Bonnie - Performs several FS type operations
dbench - Simulates NAS NetBench type load
dt - dd but can time and verify operations
IOMeter - IO characterization and measurement
IOZone - File System Benchmark Tool
xdd - Storage performance tool
vdbench - dd but better

Miscellaneous


TrueCrypt - Encrypted file/disk for Lin/Mac/Win
unetbootin - Create bootable Live USB drives
synalize - binary file editor
TeamViewer - Remote desktop viewing and control