Netstumbler is the best known Windows tool for finding open wireless access points ("Wardriving"). They also distribute a WinCE version for PDAs and such named MiniStumbler. The tool is currently free but Windows-only and no source code is provided. It uses a more active approach to finding WAPs than passive sniffers such as Kismet or KisMAC.
Download Here :: Netstumbler 0.4.0
Official Website :: http://www.netstumbler.com/