I’ve seen progress on creating WiFi Deauth buttons but this takes the cake. A ESP8266 or NodeMCU board with a OLED display that will let you attack/snoop on WiFi connections with out a Computer.
I came across this article and looks pretty darn handy. The board is only $12.00 and anywhere from 10 to 30 minutes to load on the code and deploy. However you have to be very careful with it because if you attack some one else and you could get into trouble. I honestly wouldn’t use it for evil but I would scare people with it as a teaching tool.
This would probably be a one day build and a fun toy to play with and teach with.