Retro-hardware alert:
I have written a bit about my old (and very customized) QL and only 30 years later I open sourced two pieces of the hardware:
1. a Sandy SuperQBoard clone called the "Herbert card", named after my late father. It features a floppy controller, parallel port and mouse adapter. Unlike the SuperQBoard the Herbert card is HD compatible!
2. Jochen Hassler's Eprommer-II board that can burn EPROMs and even program old GAL chips. That was pretty advanced for its time
I included current KiCAD schematics, layouts, ROMs and even source code, so everything is there to built it, enjoy!