Wikipedia
KisMAC is a wireless network discovery tool for Mac OS X. It has a wide range of features, similar to those of Kismet (its Linux/ BSD namesake). The program is geared toward network security professionals, and is not as novice-friendly as similar applications. Distributed under the GNU General Public License, KisMAC is free software.
KisMAC will scan for networks passively on supported cards - including Apple's AirPort, and AirPort Extreme, and many third-party cards, and actively on any card supported by Mac OS X itself.
Cracking of WEP and WPA keys, both by brute force, and exploiting flaws such as weak scheduling and badly generated keys is supported when a card capable of monitor mode is used, and packet reinjection can be done with a supported card ( Prism2 and some Ralink cards). GPS mapping can be performed when an NMEA compatible GPS receiver is attached.
Kismac2 is a fork of the original software with a new GUI, new features and that works for the latest versions of OS X (10.7 - 10.10, 64-bit only).
Data can also be saved in pcap format and loaded into programs such as Wireshark.