'Files' File Manager App For Windows Phone Comes To The Windows Store
Files is free to download from the Windows Store. With it, you can access files stored on your phone and SD card; browse, search, and launch files; easily share one file or multiple files; create folders to organize your files; and copy, move, rename, and delete files.

Windows Phone users seem to like the app so far -- it has a 4.5 out of 5 star rating so far based on 2,138 reviews. The only real downside is that support is limited to Windows Phone 8.1, so if you're rocking a Windows Phone device that can't run the latest release, you're out of luck. Microsoft hasn't announced any plans to make the app work on Windows Phone 8 or earlier builds.
Windows Phone 8.1 is scheduled to release on June 24, 2014. In the meantime, it's available as a developer preview, and also comes standard on a few handsets, such as the Lumia 630. If you want to download the release ahead of its official launch, you can register as a developer, whether you intend to build apps or not.