The ESP8266 has on-board WiFi and is a much more capable microcontroller (32-bit, as opposed to the 8 bits the ATmega wields).<p>A typical ESP8266 module is around $5, which is much cheaper than an Arduino (I know you mentioned the &quot;bare&quot; ATmega, but that&#x27;s going to have to go on <i>some</i> board, whereas the ESP8266 is already a PCB module, at $5).