What do you mean by Arduino app
i just wanna know Can I 'Send data, like a button press on an APP saying 'GO', which is read by the arduino Mega, via ESP8266, and send it to a particular PWM pin, say pin #2 on MEGA, to be read by other hardware connected to that particular PWM pin (#2)'
ESP8266 can work stand alone. Can switch on and off devices. I have seen it here. might as well help. http://thinkingparts.blogspot.com/2015/02/home-automation-lan-based-stand-alone.html