It states that it works for "open networks". What does that mean? All networks that you have access to? Including those in Cafes where they give you a key to lo

It states that it works for "open networks". What does that mean? All networks that you have access to? Including those in Cafes where they give you a key to log in? Or just networks that are completely open? And why does it work at all? I thought the wlan access point would encrypt the communication between itself and the computer. Would be interesting, which protocols are vulnurable to this and which are not. I guess the logging of raw wlan packets is a one-liner under linux? Does anybody know it?