Tthere are 6 boards here that are V-scored to break away. Left side is simple dip package module with some LEDs to get your feet wet soldering. the center board is a power supply for the breadboard and the right-most two columns incl. 3x BGA-PCBs (a pcb with BGA pads on the bottom) and a PCB that carries two of these 3 smaller modules.

The next 3 boards are BGA-PCBs or basically a PCB with BGA pads on the bottom side, that when you reball them, allows you to make board to board connnections without connectors. On the top side of these (in red) are LEDs, that enable us to confirm if the soldering was done properly and the connections are good.

The LEDs and resistors for the image above are all 0805s and we'll stencil these and make sure we get them reballed on the bottom side after the top side parts are in place.

Lastly is the carrier for the BGA parts. This is just landing areas for the BGA-PCBs and a breakout to a standard DIP package for the breadboard. It's a useful way to connect boards together when the boards are small enough (so warping doesn't kill it) and there is enough room on the child-board to be able to encapsulate some capability.

All of the schematics and PCB files can be found in the Github repo and are available without license to do with whatever you wish. Enjoy!