The RC522 is a 13.56MHz RFID module that is based on the MFRC522 controller from NXP semiconductors. The module can supports I2C, SPI and UART and normally is shipped with a RFID card and key fob. It is commonly used in attendance systems and other person/object identification applications.
The CNC Shield v4 is made for the control of 3D printers, milling and engraving machines. This version of the shield has 1 motor driver less than its predecessor, but is more compact and has room for an Arduino Nano. This board has 3 sockets for the installation of stepper motor drivers such as the A4988. Only 2 channels per motor are required to control this motor. There is also a connection for 2 end-stop switches per motor.
The Arduino Mega 2560 is a microcontroller board based on the ATmega2560. It has 54 digital input/output pins (of which 15 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Mega 2560 board is compatible with most shields designed for the Uno and the former boards Duemilanove or Diecimila.