In the picture from top-left, clockwise to bottom-left: the terminal block (24V power up to 13A), the 2 X-axis drivers, the Y-axis driver (blue heat sink), and the Z-axis driver (blue heat sink), the Arduino controller (direction x3/enable x3/step x3), and just below the terminal block there is a small 9V regulator board to shift 24V down to 9V for the Arduino. Everything is mounted on an MDF board, and the board is mounted with baling wire.
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/blog/show/reprap-stepper-driver-v1-2-and-next-gen-cnc