The WiFi Pineapple is a unique rogue access point. It has the capacity to use a variety of tools to trick users into connecting to it instead of other access points. It can then piggy bag its connection off of any other network connection and effectively make it self the man in the middle.
One such system is Karma. Karma listens for prob requests from your computer asking if any of its know networks are near by it and conveniently lies and says yes. The computer then connects to the pineapple by mistake and it effectively becomes the man in the middle.
Some operating system manufactures have discovered that sending open probes looking for access points is not a good idea and wont get tricked by karma anymore. To combat this the Pineapple imitates all access points in the area and those that have been probed by by other devices. It then aggressively sends out beacons saying that it is those access points which can trick some devices into connecting to it.
Along side these become requests it can also scan the network and death clients that aren’t connected to it from there current networks forcing them to connect to it instead. This can be done manually though a web interface or automatically by righting a start up script.
More info at https://www.wifipineapple.com/