From the product page:
"inSSIDer Agent is laser-focused on just your WiFi connection. This focus allows inSSIDer Agent to be very lightweight, with a clean, simple interface. It is also designed to be always-on, yet not in-your-face. The main window can be hidden, leaving just a small icon in your system tray, that will notify you when your WiFi connection changes or your computer roams to a different access point."