this is my own "interpretation" of the retro computing theme.
This thing uses an Atmega32A with an Arduino bootoader as universal I/O subsystem, "emulating" the I/O ports seen by the Z80, and the ROM too.
And with the cost of only 4$ (buying components from ebay...) it is possible to taste some flavor of retro computing...
Here is a short video:
Here all the details of the whole thing: A 4$, 4ICs, Z80 homemade computer on breadboard | Hackaday.io