Bigger screenshot
kSnoop is a simple wireless network monitor. It gathers a list of all available 802.11 networks every few seconds and displays the list along with some relevant statistics. Networks turn grey and eventually disappear as they go out of range. It can also give you a pop-up alert when an open (unencrypted) network becomes available.
How to interpret each line: After the network name, the percentage number shows the signal strength. After that, a green light indicates an "open" network, and a red light indicates a closed/passworded network. Finally, an "airport" symbol is displayed next to the network currently in use. You can mouse-over the colored status light to get a pop-up box with more info about the network, as shown in the screenshot above.
How it works: I snagged the Apple80211.h prototypes from the macStumbler folks. A small program uses that interface to pull the essential details out of the kernel, then passes them in text form to the javascript Konfabulator world. Download includes binaries for MacOS 10.3 and later, and also includes all the necessary source code (under GPL).
Unlike most other Mac software, this is not crippleware or nagware -- instead you can send me a donation if you like it:
What's all this Konfabulator stuff, anway? It's all about widgets.