I just received an ESP8266 wifi module and I am trying to add the board. However I am having an issue. All websites/tutorials say to use http://arduino.esp8266.com/stable/package_esp8266com_index.json, however nothing is there. Can it be found somewhere else?
It looks like the server is down. Isitdownrightnow reports that it's been down for almost 4 days: http://www.isitdownrightnow.com/arduino.esp8266.com.html
There is a discussion about it over on the ESP8266 forums: http://www.esp8266.com/viewtopic.php?f=26&t=3134&start=8
Let's hope it will be back again soon.