Add internet to your next project with adorable, bite-sized Adafruit ESP8266 SMT Module - ESP-12, at a price you like. The ESP8266 processor from Espressif is an 80 MHz microcontroller with a full WiFi front-end (both as client and access point) and TCP/IP stack with DNS support as well.
Adafruit ESP8266 SMT Module - ESP-12 comes with 4MB flash chip, ESP processory, and onboard antenna. These come pre-progammed with the NodeMCU Lua firmware, so you are ready to use it. Some extra parts will be needed to get this going, check out the Adafruit Downloads Link in the Documents section for the extra components recommended.
Note that Adafruit ESP8266 SMT Module - ESP-12 is intended for advanced users only. This product is just the module - which can be difficult to use. If you're looking for an easier to use version you can check Adafruit HUZZAH ESP8266 WiFi Breakout Module.
NodeMCU (Lua for ESP8266) webpage: http://nodemcu.com/index_en.html#fr_5475f7667976d8501100000f
Arduino IDE support for ESP8266: https://github.com/esp8266/Arduino
Adafruit Downloads Link: https://learn.adafruit.com/adafruit-huzzah-esp8266-breakout/downloads
Adafruit Web Site: http://www.adafruit.com/products/2491