KisMAC is an opensource and free stumbler/scanner application for Mac OS X. It has an advantage over MacStumbler, iStumbler, and NetStumbler in that it uses monitor mode and passive scanning. KisMAC supports several third party PCMCIA cards - Orinoco, PrismII, Cisco Aironet, Atheros and PrismGT. USB Prism2 is supported as well, and USB Ralink support is in development. All of the internal AirPort hardware is supported as well.