inSSIDer is FREE, open-source Wi-Fi scanning software.
Compatible with Windows XP, Vista and 7 (32 and 64-bit)
Uses the Native Wi-Fi API and your current Wireless network card
Sort results by MAC Address, SSID, Channel, RSSI and "Time Last Seen"
Compatible with most GPS devices (NMEA v2.3 and higher)
Inspect your WLAN and surrounding networks to troubleshoot competing access points
Track the strength of received signal in dBm over time
Filter access points in an easy-to-use format
Highlight access points for areas with high Wi-Fi concentration
Export Wi-Fi and GPS data to a KML file to view in Google Earth.
Filter through hundreds of scanned access points