NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting

TamoGraph Site Survey - Wi-Fi site coverage survey and modelling application

WirelessNetView - Small utility that runs in the background, and monitor the activity of wireless networks around you.

iBwave Wi-Fi - iBwave Wi-Fi software suite brings smart networking solutions to enterprise, education, hospitality, transportation, retail, office, healthcare, public venues, and residential wireless networks.

inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.

Homedale - With Homedale you can search for Wi-Fi / WLAN Access Points and monitor their signal strength.