The ESP8266 is a wireless chip with integrated 32-bit microcontroller, with costs from about 5€/piece. It has a wireless interface used for Arduino - or better yet replace Arduino. With the ESP8266 actuators and sensors can be easily realized at an unbeatable price:
The complete TCP / IP stack with WLAN connection is pre-programmed on the chip. Depending on the chip version there are several GPIO ports and an analog input. The best part is that it is supported by the Arduino development environment. Who can program an Arduino can also program this chip!