Is the package system there something that Haiku invented, or was BeOS like this as well? I had a BeOS install at one point in the 90s, but don't remember how that worked.
It's a Haiku thing. Added around 2018 if I recall correctly - see the linked lobste.rs thread in another of my comments where a Haiku developer gives some (really interesting) background on the development and effects on the community.