Some Android devices offer access to the file system, but many do not. For those in the latter category, there's Astro File Manager, a free app that developer Metago refers to as "Windows Explorer" for Android smartphones and tablets.
Astro File Manager at first launch immediately makes itself useful with an offer to manage all the files on the host device. It also presents dedicated buttons for displaying pictures, documents or music. Pressing a file-type button displays the folder(s) in which the corresponding file type exist, along with the full path. Long-pressing a folder or file presents options to copy, move, rename or delete it, or to see more information. Opening a folder with graphics files displays thumbnails, and tapping on one brings up the file in Android's Gallery or Astro's viewer, which does not support pinch zoom.
Updated on May 8, Astro File Manager works with Android 3.0 Honeycomb and higher, depending on the device. It also includes tools for file search and downloading, file and app backup, and task management. An ad-free version is available for $3.99.