Yabai (https://github.com/koekeishiya/yabai) and skhd (https://github.com/koekeishiya/skhd) together makes a very powerful combination that works extremely well. It's as close to i3 as you can get on MacOS, and outside of a few odd things with 3 monitors I haven't run into any issues.
Yabai is actually the second iteration of tiling windows that koekeishiya has made and it's super well developed.
Seconding this; the only thing I miss from i3 is the fact that yabai almost by definition can't be better integrated with the OS, so there's a slight increase in latency that's barely perceptible but enough to make me notice how much zippier my Linux boxes + i3 are. Small price to pay for how much more comfortable they make me on macOS, though.
Yabai is actually the second iteration of tiling windows that koekeishiya has made and it's super well developed.