NetStumbler
NetStumbler (also known as Network Stumbler) is a tool for Windows that facilitates detection of Wireless LANs using the 802.11b, 802.11a and 802.11g WLAN standards. It runs on Microsoft Windows operating systems from Windows 2000 to Windows XP. A trimmed-down version called MiniStumbler is available for the handheld Windows CE operating system.
The program is commonly used for:
Wardriving
Verifying network configurations
Finding locations with poor coverage in a WLAN
Detecting causes of wireless interference
Detecting unauthorized ("rogue") access points
Aiming directional antennas for long-haul WLAN links
No updated version has been developed since 2005.
Alternatives
InSSIDer was created as an alternative to Network Stumbler for the current generation of Windows operating system.
Kismet or LinSSID for Linux, FreeBSD, NetBSD, OpenBSD, and Mac OS X
KisMAC for Mac OS X
Vistumbler was created as an Open Source alternative which supports Windows Vista (hence the 'Vis' in the name of the program), Windows 7 and Windows 8