How-To Geek

access ReiserFS partitions in Win : rfstool
analyze network traffic : Analyzer
analyze network traffic : BO2K
analyze network traffic : Show Traffic
analyze network traffic : Ethereal
analyze network traffic : WinDump
analyze server log files : Analog
analyze/audit network security : Nmap/Network Mapper
audit computer software and configuration : OCS Inventory NG
change directory fast : WCD
check md5 checksums : MD5summer
clone a hard disk : g4u
completely wipe/delete a hard disk : Darik's Boot and Nuke
completely wipe/delete a hard disk : Eraser
display free RAM : RAMpage
display system information : CoolMon
display system performance metrics : Rainmeter
display system process information : Process Trace
graphically view linux partitions and files : Explore2fs
graphically view linux partitions and files : YAReG
log network traffic : daSniff
monitor internet connections from applications : Winpooch
monitor smart hard drives : smartmontools
partition a hard disk : Partition Logic
recover lost partitions : TestDisk
recover lost partitions on a drive : TestDisk
remotely access event log information : Snare Agent for Windows
remotely control another computer : EchoVNC
remotely control another computer : UltraVNC
remotely control another computer : TightVNC
remotely see network properties : NetBIOS
run a linux-like environment in windows : Cygwin
scan TCP security ports : Knocker
search network traffic : ngrep
synch files between win and unix : Unison
test memory : Memtest86
use a dynamic DNS / fixed hostname address : Dynksys Dynamic IP Updater
use a dynamic DNS / fixed hostname address : MyDyndns
use a dynamic DNS / fixed hostname address : DeeEnEs

Another good Registry Cleaner that is freeware is Regseeker.

Link: http://www.hoverdesk.net/freeware.htm