There have been plenty of Z80 computer builds here on Hackaday ... Programs can be loaded through embedding an assembly listing into the Mega’s sketch, or, once the debugger is up you can ...

and a very simple getting started and assembly guide. The simplicity of the design becomes obvious from the chip count, there’s the Z80 itself, a 6850 UART, 27C512 ROM, 62256 RAM, 74HCT04 for ...

It was called the Z80 SoftCard, and it was first released 43 years ago this month, on April 2, 1980. In an even more ironic twist, the product was made as an add-in card for the Apple II PC.