I use Mac, Windows, and Linux, but I use the same USB drive for all of my files, formatted NTFS. I'd like to tag my files in such a way that no matter which OS I'm using, I can search for my files, explorer them, and preview them the same way.
I don't mind using a special app for exploring and previewing, but I'd much rather integrate Mac Spotlight comments, Windows file tags, and Linux Beagle tags so that I can browse files using the OS's native file explorer program.
Did you have a particular program in mind for this? The majority of applications on this site were not developed by people on this site. Most are packaged versions of other FOSS and Freeware.
Edit: I may have been too hasty. I think a better place for this would be "General Discussion", especially if you didn't have a program in mind already.