Developer website: Pierce T. Wetter III
This is a version of GrandPerspective tweaked so that if applied to a Time Machine drive, it treats any file with outstanding hard links as having zero size.
This is useful for looking at your TimeMachine backups and seeing what files you might want to exclude from the Time Machine backup, because the file is constantly changing. For instance, lets say you have a 10GB database file that changes by 1K every hour. Time Machine will have to back up the entire file everytime, just because 1K changed. So that's 240GB over a 24 hour period.
When I used it today, I found out that /var/db/RemoteManagement/caches/ was backing up a 6GB filesystem.cache file each backup! So I added /var/db/RemoteManagement to my exclude list in TimeMachine. You can see that in the enclosed screenshot, all the orange squares above are that giant file.
Note: I didn't write the tool, Erwin Bonsma did, and since he made it open source, I just tweaked it.