Folder Synchronizer helps create and keep folder copies on many devices, such as USB drives, SD cards, portable HDD, inner smartphone memory, etc. The app a) compares two folders, b) displays the differences statistic and c) makes the target folder equal to the source folder.
It's very helpful to
1) backup of your files
2) share your photos and videos with your parents and friends
3) keep identical copies of music, photo and video on smartphone, tablet, media player, etc.