X-Micro Arduino, Raspberry Wifi Serial Transceiver Module with ESP8266 Chip

ESP8266 is a highly integrated chip designed for the needs of a new connected world. It offers a complete and self-contained Wi-Fi networking solution, allowing it to either host the application or to offload all Wi-Fi networking functions from another application processor and it has a powerful on-board processing and storage capabilities that allow it to be integrated with the sensors and other application specific devices through its GPIOs with minimal development up-front and minimal loading during runtime.
 
Interface:

SDIO 2.0, SPI, UART
32-pin QFN package
Integrated RF switch, balun, 24dBm PA, DCXO, and PMU
Integrated RISC processor, on-chip memory and external memory interfaces
Integrated MAC/baseband processors
Quality of Service management
I2S interface for high fidelity audio applications
On-chip low-dropout linear regulators for all internal supplies
Proprietary spurious-free clock generation architecture
Integrated WEP, TKIP, AES, and WAPI engines
 
Specification:

802.11 b/g/n
Wi-Fi Direct (P2P), soft-AP
Integrated TCP/IP protocol stack
Integrated TR switch, balun, LNA, power amplifier and matching network
Integrated PLLs, regulators, DCXO and power management units
19.5dBm output power in 802.11b mode
Power down leakage current of Integrated low power 32-bit CPU could be used as application processor
SDIO 1.1/2.0, SPI, UART
STBC, 1×1 MIMO, 2×1 MIMO
A-MPDU & A-MSDU aggregation & 0.4ms guard interval
Wake up and transmit packets in Standby power consumption of