Redux-inspired and built on top of RxJs, NgRx Store is a reactive fashioned application state management for Angular. It's not the only one out there, yet it might be the most comprehensive and popular choice for the goal.
It's a great tool that helps to keep the application state in one place. It makes it easy to keep track of events and the side effects of those events.
It comes with mocking tools which makes it highly unit testable and a developer tool under the hood that allows you to use the Redux Devtools Extension for Chrome and Firefox which makes it simple to trace and visualize actions and debug.