It is a plugin for the music player DeadDBeeF, it adds an entry "Playlist Manager" to the context menu. It can remove duplicate and vanished files from the current playlist or synchronize a playlist with a directory including subdirectories. This will remove deleted files and add new ones to the playlist. Changed files are not recognized, such changes would have to be updated manually via "Reload Metadata" in DeaDBeeF.
When using the plug-in for the first time, a directory must be selected with which the playlist is to be synchronized. This directory is saved permanently and does not have to be specified again later, but can be changed at any time with "Select Folder", the option "Reset Folder Tag" is to remove the directory from the settings.
To compile the plugin you need to copy the file deadbeef.h from the deadbeef directory. After that you can create the plugin using make. After successful creation, there are two files named playlist_manager_gtk2.so and playlist_manager_gtk3.so in the directory. Copy one of the two files, depending on whether you want to use the GTK2 or GTK3 version, into the plugin folder (~/.local/lib/deadbeef/) and restart DeadDBeeF.