Wikipedia
NetSpot
NetSpot is a software tool for wireless network assessment, scanning, and surveys, analyzing Wi-Fi coverage and performance. It runs on Mac OS X 10.6+ and Windows 7-8-10 and supports 802.11n, 802.11a, 802.11b, and 802.11g wireless networks. NetSpot 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 that. NetSpot was released in August, 2011 and available at MacApp Store.