Sloth is an open source program developed for Mac users who wish to learn information about all of the files that are opened on their systems. This utility might prove to be of good use if you need to know exactly which applications are using which files.
Once you launch the tool on your computer, it automatically scans your system and provides you with a list containing all open files. The files are nicely organized based on the program that's using them. For instance, under the iTunes category you will find files from the folders like Resources, Fonts, Extensions, and many others.
The application comes with an integrated search tool to help you immediately find the opened file you need. You can sort the results by using the filters from the upper side of the main window.
Another great thing about this utility is the fact that it helps you kill running processes. This features comes in handy whenever a running process is unresponsive and you need to immediately shut it down. Also, it provides you with quick access to the home folders of any of the listed opened documents (it reveals the file in the Finder program).
The app doesn't require a help guide as its interface is very intuitive and you can easily handle it, even if you have little computer experience.
Personally, I can't find a single flaw in this program. It does exactly what's being stated on the homepage of the developer, it is very simple to handle, and it's free. So, you should definitely give it a try if you need to learn more about the opened files from your Mac.