Why can't iStumbler see my network?
iStumbler scans by sending out probe frames over the Wi-Fi interface on all available channels. Access Points MAY respond to these probes but they might also be configured as private networks. iStumbler can now see any network you are connected to, if it's responding to probes or not. iStumbler is intended to find publicly available wireless. Making your network private is the equivalent of putting up a "No Trespassing" sign and the tool respects that.

Does iStumbler allow me to access networks protected by WEP?
No. A few have asked for this feature but I don't plan to implement it. You can use KisMac for that. iStumbler is intended to be an easy to use tool for finding open, public networks. While the ability to test your security setup is useful, it's out of scope for this tool.

What do the abbreviations mean?

• WEP = (Wired Equivalent Privacy) a form of layer-2 encryption
• SSID = (Select System IDentifier) the network name
• IBSS = (Independent Basic Service Set) an ad-hoc network
• BSS = a managed infrastructure network
• MAC = (Media Access Controller) unique hardware address

Does iStumbler support wireless interfaces other than built-in Wi-Fi?
Not yet.