. It is an ingame plugin manager.
Pluginmanager loads all the plugins you have selected for it when it starts.
So start it once with /plugin load manager, then click all the plugins you want load and then apply.
Move whatever is in your first hotkey slot and type /shortcut 1 /plugin load manager. This will create a hotkey that you only have to hit when you start the game. It will load all the plugins you have then.