I'm the author of TMSU. If you've not heard of it before it's my pet project that lets you tag your files (from the command line) and then mount a virtual filesystem that lets you access them, by tag, from any other program, including those with graphical interfaces.
I've just released version 0.5.0, which has a number of new features and bug fixes. This version also provides a Windows binary for the first time, though it's a bit buggy at the moment and doesn't include a virtual filesystem (I'm working on that).
Usage goes something like this:
$ tmsu tag photo.jpg holiday country=spain year=2014 family
$ tmsu tag song.mp3 music big-jazz good
$ tmsu files music
song.mp3
$ tmsu files "year > 2010 and holiday"
photo.jpg
You can bring up a virtual filesystem like this: $ mkdir mp
$ tmsu mount mp
$ ls mp/tags
big-jazz country family good holiday music year
Feel free to ask any questions and I'll do my best to answer them. Thanks for your time!• Homepage: http://tmsu.org/
• Project: https:/github.com/oniony/TMSU/
• Download: https:/github.com/oniony/TMSU/releases/0.5.0