I finally got sick of using Activity Monitor on macOS since it uses too much resources and am making good on a promise I made earlier to rewrite it: https://news.ycombinator.com/item?id=25401791. It just needs some XPC refactoring but other than that it's at the point where I just never use Activity Monitor at all anymore, so I'll probably put the source up soon. I have a bunch of things in mind in the future that fit in with the goal of answering the question of "why is my Mac slow" that has so far either existed in scattered tools or not been easy to gather data on at all.