aircrack is an 802.11 WEP and WPA-PSK keys cracking program that can recover keys once enough data packets have been captured. It implements the standard FMS attack along with some optimizations like KoreK attacks, thus making the attack much faster compared to other WEP cracking tools. In fact aircrack is a set of tools for auditing wireless networks.
Aircrack-ng is the next generation of aircrack with lots of new features (planned and wanted).
Aircrack is useful and I have found it real good for WiFi Audting with a Windows PC's. I figured I would drop the link here as it is getting harder and harder to find links to it.