Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and (with appropriate hardware) can sniff 802.11b, 802.11a, 802.11g, and 802.11n traffic. Kismet also supports plugins which allow sniffing other media such as DECT.

Kismet identifies networks by passively collecting packets and detecting standard named networks, detecting (and given time, decloaking) hidden networks, and infering the presence of nonbeaconing networks via data traffic.

Tue Jan 12 2010 - Kismet-2010-01-R1 released, find it here. Includes fixes to segfaults, compiling problems on Snow Leopard, GPS, and sundry other quirks, and enhancements to the UI, support for the new GPSD JSON-only protocol, and a BT scanning plugin for BT device discovery.

Sun Nov 29 2009 - Kismet-2009-11-R1 released, in the usual place. Release includes fixes to crashes on resizing terminals, tweaks to plugins, addition of the autowep plugin, improved plugin handling, plugin support on OSX, initial support for Snow Leopard, fixes to PPI corruption, XML fixes, and quite a lot of other bugfixes.

Wed Jun 24 2009 - Kismet-2009-06-R1 released! See the downloads page per usual. Lots of fixes in this one (including dropping the 'candidate' designation), see the list here.

Thu Jun 18 2009 - Spectools 2009-06-R1 released! Some bug fixes, plus support for the new Wi-Spy 24i device

Wed May 29 2009 - In a moment of short-lived glory, Kismet-2009-05-RC2 is now out, again on the download page. Downloads for RC1 have been redirected to RC2. 2009-05-RC2 fixes a 1-character bug which led to corrupted logfile names and bad kismet_server launching.

802.11b, 802.11g, 802.11a, 802.11n sniffing
Standard PCAP file logging (Wireshark, Tcpdump, etc)
Client/Server modular architecture
Multi-card and channel hopping support
Runtime WEP decoding
Tun/Tap virtual network interface drivers for realtime export of packets
Hidden SSID decloaking
Distributed remote sniffing with Kismet drones
XML logging for integration with other tools
Linux, OSX, Windows, and BSD support (devices and drivers permitting)

For more detailed development information than the changelog or news provides, general wireless info and link-whorery, and other stuff, check out the development blog here.

Presentations from various talks I've given are here.

Screenshots of the Panels UI and GPSMap mapping tool are here.

Stop by #kismet on irc.freenode.net.

The open source tools for the WiSPY Spectrum Analyzer are on the WiSPY page here