A while back I remember seeing a simple ESP8266 wifi jammer, it announces a huge number of APs with random names, making it hard for devices to connect to real networks:
http://ruralhacker.blogspot.pt/2016/01/esp8266-jamming.html
things have GREATLY IMPROVED , newly realeased jammer can to selective deauth from 5$ wifi module
Deauthentication attack and other ‘wifi hacks’ using an ESP8266 module.