ESP8266 is a single chip cpu/wifi solution that is very cheap and a good alternative to arduino if you want to use WiFi. Read more here:

ESP8266 on wikipedia

Datasheet, sdk and forum from Espressif (the producer)

Post here at related to  ESP8266:

(Note that older posts will be in danish)

IHC Soap client for esp8266
ArduinoIHC now in library manger
Sonoff touch and new DingSwitch 1.1
DingSwitch - en esp8266 basseret stikkontakt til IHC
Sonoff s20 - den orginale
Sonoff S20 - klon
Broadlink smart switch
Sonoff - wifi styret relæ
DFPlayer mini mp3,wav lydmodul
USB til RS232 TTL
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