Dash is a commercial software on macOS. The author created the whole docset parsing/plugin stuff and markets the tool. I use it for years and upgraded multiple times since it’s a timesaver.

There has been controversy in the past about the tool since it is a glorified man page reader. The author even shared at one point his earnings and what he is doing with it.

And no there is no zeal for macOS. I don’t know the details behind that deal. I can only say that zeal is not as good as dash. The integration into macOS is way smoother than what one gets on windows and Linux. I tried all versions.