The MiSTer FPGA project has developed several add-on daughter boards these are plugged directly into the DE10-Nano main board expanding its capabilities.

If you enjoy soldering and the satisfaction of building your own MiSTer FPGA add-on boards from scratch, bare PCBs without any components are available for purchase. Buying just the PCB is great if you want to source the required components yourself and are confident with a soldering iron.