[PaulHoule]

See also

https://www.commanderx16.com/

Which is based on the 6502-compatible 65C816 but used a simple banking scheme instead of the broken 24-bit address space that chip natively supports (no 24-bit index registers) The way video memory works in it is really clever and lets it really surpass 1980s machines in many ways.

My favorite retrocomputer though has to be

https://www.olimex.com/Products/Retro-Computers/AgonLight2/o...

which is priced right though it doesn't have the keyboard and instead based on the eZ80 which really does extend the Z-80 with 24-bit registers so that you can use all the RAM easily.

[CTOSian]

The guys behind Olimex are top chaps! Their products are not only affordable, also OpenSource as well! Nothing good came so far by the C= or Amiga copyrights...

[snvzz]

I think a better comparison would be with e.g. the miSTer and the many cores its ecosystem maintains, all open source HDL.