Caveat: 60p RP2350 microcontroller on a board that sells for $40 and has 8MB of RAM (as opposed to the 520K that the RP2350 comes with). But that is only needed for Photoshop. The 520K is more than enough to emulate the Mac 128K.

I'm reminded that chips like the Intel 8080 and Motorola 6800 were not intended to be general-purpose computers, and were originally designed mostly to be embedded controllers and as building blocks for "real" computers like terminal and disk controllers.

I suppose in principle the RPi Pico could self-host its own OS and devel environment. 520 KB of RAM in the old days was plenty to fit an OS and compiler. No MMU so no paging though.

For a more capable but still underpowered computer, I found Antix can run well in almost 20year old hardware - I use it in an EEEPC 4G Surf, but I modded it to have more storage recently.

Black and white photoshop, yes.