Small transceiver module Wi-Fi-based chip ESP8266, compatible with standard 802.11 b / g / n 2.4 GHz, has SPI interface, 7 GPIO, TCP / IP stack and antenna ceramic PCB. Ideal for wireless sensor networks, home automation, building automation, and custom applications. Power: 3.3 Vdc, dimensions (mm): 17.4 x 12.2.

• 802.11 b/g/n
• Ceramic Antenna
• Wi-Fi Direct (P2P), soft-AP
• Stack TCP/IP integrated
• + 19.5dBm output power in 802.11b
• SDIO 1.1/2.0, SPI, UART
• STBC, 1 x 1 MIMO, 2 x 1 MIMO
• A-MPDU & A-MSDU aggregation & 0,4 ms guard interval
• Wake up and packets trasmission: < 2ms
• Integrates WEP, TKIP, AES e WAPI
• Communication interface voltage: 3,3 Vdc
• Standby consumption: < 1 mW (DTIM3)
• Dimensions (mm): 17,4 x 12,2
• Weight: 3 grams

• https://github.com/esp8266/esp8266-wiki/wiki