Itβs a simple no install application that can work from any usb device aswell and supports Windows OS.Just launch the application and it will first auto scan for the available networks and shows a list of available networks both secure and open, and tries to automatically connect to the open network.
It shows the Network name, Signal Strength, and Encryption (If any used) or Open for open networks.
Also read How you can protect yourself while using public wifi hotspots.
Note : Windows XP needs Wireless LAN API if outSSIDer fails to connect and .NET 2.5 if it fails to launch.
Download Outssider β wifi scanner