Sloth is an OS X application that displays a list of all open files and sockets in use by all running applications on your system. This makes it easy to see which apps are using which files and sockets.
Sloth is basically a GUI application on top of the powerful
lsof command line tool. The output of
lsof is parsed and shown in a searchable, filterable table view with some convenient user friendly functionality such as revealing files in the Finder, killing a file's owning process, etc.
You can download the app here:
Sloth is open source software and has a home on GitHub.