NirSoft develop many free utilities for Windows, here is a list of the best ones:
Wireless Network Watcher scans your wireless network and displays the list of all computers and devices that are currently connected to your network
WirelessKeyView recovers all wireless network security keys/passwords (WEP/WPA) stored in your computer
ProduKey recover Product ID e key of Microsoft Office (2003/2007), Windows (Vista and 7 included), Exchange Server and SQL Server
CurrPorts display TCP/UDP ports currently in use by programs and processes
WebVideoCap captures Flash videos and RTSP/MMS streams to watch them later
RTMPDumpHelper it allows to capture and download audio/video RTMP streams
SearchMyFiles it extends stadard files search feature in Windows
RunAsDate it allows to run a program within a specific date/time