Quantum Mini Linux Development Kit
Quantum Mini Linux Dev Kit is possibly the smallest Linux development board on the market, a highly integrated kit with quad-core CPU that can run Linux at only 40mm x 35mm, which also includes network connectivity. It is suitable for scenarios such as as a personal server, intelligent voice assistant, and for robotic development.
The SoM is called Quark-N, based on Allwinner H3, Quad-core Cortex-A7, and ARM Mali400 MP2 GPU. The 6-layer high-density gold PCB design integrates a complete ARM-Linux system (CPU, DDR, eMMC) in a 2x3cm space. Also, most of the GPIO is led out by the board through the M.2 Key-A golden finger interface to minimize the bottom board design difficulty. You can easily design your own base plate with two-layer boards to realize your interesting ideas.
https://wiki.seeedstudio.com/Quantum-Mini-Linux-Development-Kit/