Windows: The Bluetooth interface built into Windows is Spartan compared to the feature rich Bluetooth Radar, an open-source application that displays all Bluetooth devices within reach of your computer's radio on a radar-style display.
Bluetooth Radar displays both paired Bluetooth devices — devices linked to your computer — and unpaired devices just floating around within reach of your Bluetooth radio. Bluetooth Radar retrieves basic information from the unpaired devices but in the case of paired devices gives you additional options like file transfer and remote file browsing.
Bluetooth Radar is open-source, Windows only. Have a favourite trick or tool for getting the most out of Bluetooth and your wireless devices? Let's hear about it in the comments.