Didn't know this existed. I'll definitely consider it if I ever go back to using Windows.

I didn't spend enough time to verify if it satisfies the "can use other clients" and "can add 3rd party repositories" criteria. But assuming it does, I bet tons of people would happily use it, if Microsoft blessed it as the official standard for managing Windows applications / installed it by default.

The official package manager of windows is winget.

https://github.com/microsoft/winget-cli

I like scoop though personally.

https://scoop.sh

I didn't use windows for a few years but last time I tried everything I needed was in the main repo - it feels similar to brew but less popular among windows users.

In combination with the ChocolateyGet provider for Powershell this works pretty well actually. It's not apt-get or similar, but it does get rid of the point-click installation for quite a lot of common software.