zlacker

http://ticalc.org used be my go-to site in the 90s. Still active, too, a post as recently as yesterday (2019-11-25). Lots of good games there. Also, a lot of Z80 assembly reference and links to emulators. If you like classic Super Mario, definitely checkout Penguins. There's also some Zelda clones, nibbles/snake.

There used be a Monopoly clone, but that's gone. Allegedly the trademark owner (Parker Brothers at the time IIRC) went after the developer for trademark infringement and he had to take it down. But, rather than sue them, PB actually hired the dev to make the original Game Boy Monopoly game. No idea about the veracity of this, but just a vague recollection from the 90s.

I actually still have my dead-tree Z80 instruct set reference manual sitting on my shelf at home next to my 68K manual. 2 of my oldest and well used programming references.