Wikipedia
IStumbler
iStumbler is a utility for finding wireless networks and devices with AirPort- or Bluetooth-enabled Macintosh computers.
iStumbler was originally based on MacStumbler source code. Its early development focused on detection of open wireless (802.11) networks, but more recent versions support the detection of Bluetooth wireless devices and Bonjour network services.
Up to release 99, iStumbler was open source under a BSD license.