It's a real nice tinker toy for only a few pounds/dollars.

The default firmware uses modem-style 'AT' commands for control, but there is an Open Source LUA implementation, and you can cross-compile in C.

http://www.esp8266.com/

https://github.com/nodemcu

http://l0l.org.uk/2014/12/esp8266-modules-hardware-guide-got...