The D1 R2 is a mini wifi board based on ESP-8266EX.
11 digital input/output pins, all pins have interrupt/pwm/I2C/one-wire supported(except D0)
1 analog input(3.3V max input)
A Micro USB connection
A power jack, 9-24V power input.
Compatible with nodemcu
The D1 R2 has a micro USB for auto programming.
Also you can programming it using OTA
All IO is work at 3.3V.