The CJMCU card is a small microcontroller based on the ATTiny85 chipset. It is perfect for wearable projects. Also widely used in electronic projects due to its compatibility with the Arduino IDE, bringing an ATtiny85 and the necessary circuits to be programmable via USB.

Specs:

8K Byte of In-System Programmable Program Memory Flash
512 Bytes In-System Programmable EEPROM
512 Bytes Internal SRAM
Diameter:25mm

Link to use it to add the boards to the Arduino IDE: ClickHere

Link to Digistump Drivers: ClickHere