This is basically what Zack mentioned in the video. 
I attached the Fusion360 file so you can go nuts with it. 
This upload contais a 1x3 and 1x2 Model.

Update 2023-01-04:
Added versions without the magnetholes in the bottom, because its uses less material and prints faster. If you dont plan on using magnets, use the version without holes.

Credit go to
DrDflo: https://thangs.com/designer/DrDflo/3d-model/Engineer's%20Desk%20Organizer-37318 
Zack Freedman for the open source design of the #Gridfinity https://thangs.com/designer/ZackFreedman