Everything is a PLUGIN in Remix
In order to integrate new tools made by us and by ...you into Remix, we've now made everything a plugin. This architcture will also allow Remix or just parts of Remix to be integrated into other projects (your's for example).
This means that you only load the functionality you need.
It also means that you can turn off and on plugins - as your needs change.
This all happens in the plug manager.
The Plugin Manager is also the place you go when you are creating your own plugin and you want to load your local plugin into Remix.
To load your local plugin, you'd click on the "Connect to a Local Plugin" link at the top of the Plugin Manager panel.
To learn more about how to create your own plugin, go to the README of remix-plugin repo.