This is a low cost for Arduino-compatible ESP8266 development board. A 0.96″ OLED display is on the board. It is very easy for beginners. You can program it like for Arduino. There is a project support for ESP8266 chip to the for Arduino environment: for Arduino core for ESP8266 WiFi chip. Another famous project is NodeMCU, which you can use LUA to control ESP8266.
Specifications: 
All ESP8266 pins broken out
12 digital pins write/read/interrupt/pwm/I2C/one-wire supported(except D0)
1 analog input
Integrated 0.96 Prime. OLED
Micro USB connection
Compatible for Arduino
Compatible with NodeMCU(Lua for ESP8266)
Input Power 4.75V ~ 12V
Size: 6.2×2.7cm/2.44×1.06inch