WhatsOpen is a MacOSX utility designed to aid you in determining what is holding your files open. There is a common OSX error when trying to eject removable media relating to files being in use. Often times your files are in use by Spotlight or some other internal system and you don’t even know what program to kill to free up the files and allow the media to eject. This utility makes that a snap. It also provides many other administrative features you may find useful.