Ask HN: What platforms to emulate between Chip-8 and GameBoy?

After writing an emulator for Chip-8, most recommend emulating GameBoy. Let's suppose I'd like some intermediate options. What would they be?

Maybe. Wikipedia page for 2600 mentions Fairchild Channel F, which is even simpler. It also gave me an idea to look at "List of early microcomputers" on Wikipedia.