Linus Åkesson (previous mentions) presents a simple hardware project, and a clever software project, to build an autobooting C64 cartridge on single-sided board. Built this way, the address lines are not available, but by cycle-counting and using a multi-stage bootstrap, all is well. (Some small improvements arise in the comments):
Here’s the hardware - the stripboard plugs directly into the cart port, the conductors all being on the underside:
Nearby on his site, and not related, but still retro, a very quick video tour:
The evolution of C64 games 1982–2023
Also nearby, and even less related, a remarkable Amiga-like demo platform written in 17000 lines of bare metal RISC-V code for the Pico 2:
Kaleidoscopico (detailed technical blog post)
