Specs:

• Measures 2.0″ x 0.9″ x 0.28″ (51mm x 23mm x 8mm) without headers soldered in
• Weight: 9.7 grams
• ESP8266 @ 80MHz with 3.3V logic/power
• Stacking headers
• Contains Tensilica chip core
• 4MB of FLASH (32 MBit)
• Built in WiFi 802.11 b/g/n
• 3.3V regulator with 500mA peak current output
• CP2104 USB-Serial converter onboard with 921600 max baudrate for uploading
• Auto-reset support for getting into bootload mode before firmware upload
• 9 x GPIO pins – can also be used as I2C and SPI
• 1 x analog inputs 1.0V max
• Built in 100mA LiPoly battery charger with charging status indicator LED, can also cut a trace to disable the charger
• Pin #0 red LED for general purpose blinking. Pin #2 blue LED for bootloading debug & general purpose blinking
• Power/enable pin
• 4 mounting holes
• Reset button
• Includes connector for any 3.7V Lithium polymer battery
• Programmable using the Arduino IDE for an easy-to-run Internet of Things core

Check out Adafruit’s tutorial for details, schematics, files, IDE instructions, power management and more.