Unity File Explorer is a Unity package that allows the visualization and use of the local file explorer as UI during the Unity runtime. The UI can be defined through prefabs and is highly customizable.
Download the package through the Window > Package Manager in the Unity Editor with Add package from git URL.... Using the URL https://github.com/FKI-HTW/UnityFileExplorer.git#upm for the newest version, or https://github.com/FKI-HTW/UnityFileExplorer.git#VERSION_TAG for a specific one. The available version tags can be found in Tags.