Kismet is an open source Wi-Fi stumbler, packet sniffer, and intrusion-detection system that can run on Windows, Mac OS X, Linux, and BSD. It shows the AP details, including the SSID of "hidden" networks. It can also capture the raw wireless packets, which you can then import into Wireshark, TCPdump, and other tools. In Windows, Kismet only works with CACE AirPcap wireless adapters due to the limitation of Windows drivers. It does, however, support a variety of wireless adapters in Mac OS X and Linux.