NetSpot 1.0 (http://www.netspotapp.com/) is a new, free app that lets you conduct a wireless site survey of almost any complexity for free. It’s compatible with Mac OS X 10.6.x and 10.7.x
NetSpot allows collecting, visualizing and analyzing Wi-Fi data using any Apple laptop. It lets you conduct a wireless site (WLAN) survey of almost any complexity without the need of purchasing specific hardware.
All you have to do is to take your MacBook, load your area map, point your location on the map and NetSpot starts collecting Wi-Fi data around you. The software uses the standard Wi-Fi network adapter and its AirPort interface to map radio signal strength and other wireless network parameters and build reports on top of that. It lets you see how your wireless network operates in your office, house, campus, cafe, airport, or just about any building or area.