Aircrack-ng - WiFi Network Security Suite (Monitoring, Attacking, Testing, and Cracking)
Aircrack-ng is an amazing set of tools that can monitor, attack, test, and crack WiFi networks. Yes, it can crack WiFi passwords, supports WEP and WPA PSK (WPA 1 and 2)!
If you are going to use Aircrcak-ng on a windows machine, then Good Luck with that.... Because Windows doesn't fully support this security suite. So, use a Linux machine if you really want to do something with Aircrcak-ng.
Before running the tools on your computer, you must read the Getting Started page to know the basic stuff.