WEMOS D1 is a WIFI development board based on ESP8266 12E. This functioning is similar to that of NODEMCU, except that the hardware is built resembling Arduino UNO.
This D1 board can be configured to work on the Arduino environment using BOARDS MANAGER.
So, it’s not necessary to use a separate Arduino board, This D1 itself can be programmed on Arduino IDE. This is handy in using IoT projects. Further many Arduino SHIELDs are compatible with This D1 board.
Different versions of D1 boards are available in This market  R1, R2, MINI
As the name implies D1 Mini is a smaller version
R1, R2 boards look like the Arduino UNO board, but a version is not printed on board. On some boards, WEMOS D1is printed, as the ESP12 chip is manufactured by WEMOS.
In some other boards, it is printed just D1,where the ESP12 chip is that of AI Thinker.
