The Windows Phone app which has gone free next as myAppFree app of the day is Files&Folders Pro.This is a fully functional file manager for Windows Phone 8.1 .
Files&Folders Pro Features:
1. File and folder options (copying, moving, renaming, deleting)
2. Opening and extracting files from archives (RAR, ZIP, 7z, ZipX, ISO, BZIP2, GZIP, TAR, ARJ, XZ, CAB…)
3. OneDrive support
4. Dropbox support
5. Adding folders to Favorites and pinning them to the Start Screen
6. Themes and backgrounds, Bing wallpaper