On Mac I use WiFi Explorer.

Even on the Standard version I find the Channels view to be highly useful. Seeing what other WiFi sources are conflicting with the channels being used by my own gear really clarifies what channels I need to NOT be using.



I can carry my MacBook around like a Geiger counter and sniff out which sides of the house (and which neighbours) are squatting across precious bandwidth. In some cases I offer to adjust their own WiFi gear to better channel selections (for both of us) and turn off 2.4Ghz wide channel modes.