Kismet is an 802.11 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring mode, and can sniff 802.11b, 802.11a, 802.11g, and 802.11n traffic (devices and drivers permitting).

Kismet also sports a plugin architecture allowing for additional non-802.11 protocols to be decoded.

Kismet identifies networks by passively collecting packets and detecting networks, which allows it to detect (and given time, expose the names of) hidden networks and the presence of non-beaconing networks via data traffic.

For information on how to compile, install and use Kismet, see author's readme.

Requirements:
OS X
GNU Make (to build from source)