WiFi Explorer is a general Wi-Fi stumbler developed by Adrian Granados, available for $6.99 via the App Store. It runs on Mac OS X 10.7 and later. It only works with the internal AirPort card; USB Wi-Fi adapters aren’t supported. Once you open WiFi Explorer, you immediately see the list of SSIDs on an attractive GUI. You’ll see the usual network details, including noise and SNR, and can add/remove more details via right-clicking on the columns. By default, the signal levels are shown in percentages, but you can change to dBm via the Preferences. Accessing the Help brings up a traditional help window, containing great documentation, which is also accessible off-line. It includes some good general Wi-Fi troubleshooting information as well.