clickteam fusion has had a builtin plugin manager for ages
All the plugins that are listed in it are free.
it's right in the editor- it lists, updates and downloads plugins to your project with zero configuration needed by the user.
Separately they also have a store, which is used for premium plugins
Godot also recently got a plugin manager that gets them straight from github.
Most game engine editors nowadays have a built in plugin manager that can fetch them from a repository.
Construct2 has lots of community made plugins and even a couple of community made managers - but scirra has not done anything about managing them - so some of them are now on dead links. The editor has no infrastructure made for fetching plugins from an official repository!
I find the lack of a plugin manager strange and would love to see construct3's editor finally get one