Dirk Grappendorf made this DIY computer based on 8-bit MOS 6502 CPU that was used in many popular home computers of the 1970s and 1980s like the Commodore 64 or the Apple II with 3d printed case.
He has detailed documentation so you can go step by step and make it yourself.
Project homepage: http://www.grappendorf.net/projects/6502-home-computer
All the files and code needed for this project can be found here:
If you find this interesting check out the Pi Top project.