Witty is the latest version of the all-in-one development board for the hugely popular WiFi IoT chip from Espressif, the ESP8266. The main PCB on top consists of an ESP-12F module along with an RGB LED, an LDR, a user push button and USB connector for power. The bottom board has a CH340G USB-to-UART module that allows you to connect this board to your PC/Laptop to reprogram the flash or to see debug messages. The real advantage of this design is that, once your firmware is ready to be deployed into a project, you can remove the bottom board and directly power the top board (either through the additional USB connector or connecting power to the pins).
All the pins of the ESP-12F are brought out, so this module is just as flexible as the bigger Nodemcu board while being more compact and cheaper. You can use the nodemcu firmware, or the Arduino development environment or build your own firmware using Espressif's SDK for the ESP8266. You will need to program the firmware of your choice at the beginning before you are able to use this module.