Raspberry Pi, I suppose. But it doesn't feel the same, but the Pi is really underpowered compared to the average phone/computer, while the ZX Spectrum was the most powerful, and only, computer millions could afford.

I recently had the feeling of those early home-computing days from the Ben Eater's "8-bit computer from scratch" videos/kits. Really fun project: https://www.youtube.com/watch?v=HyznrdDSSGM&list=PLowKtXNTBy...