TagSpaces has excellent GUI support.

That looked excellent until I read that it stores the tags in the filename. That's just... completely not what I'm looking for, or would use, ever.

Yes, it's a trade-off; or you keep the tags in a database on which you are dependent or you store everything in the file name or the file itself. Tagging inside the file can only be done if the filetype has support for it (exim or mp3 tags) and you have to program support for the different filetypes. Keeping it in a database necessitates a sync step between moving and renaming actions in the filesystem and the database itself and has to be programmed and tested for every OS. By keeping the tags in the filename, this way this tag system still keeps working without the tooling itself and across operating systems, but you have to give up some freedom in the naming of your files (so it doesn't really work on DOS). Why wouldn't you use such a system ever? People accept metadata in the file itself, the file name usualy describes the data - so why not use tags in the filename other then that it seems ugly hack? How are the alternatives better?

Was thinking "I like this but no Windows" so thanks for referencing TagSpaces, gonna try it right now

Thanks, I downloaded it.