App for tagging a list of Steam games?

So... does anyone know of a good app that can tag generic lists?
In this case, I'd want to use it to tag the games in my Steam Library, since Steam still can't do that.
I started using this site, but it's lacking too many features that I want (multi-select, partial tag match, exclusion filters, auto-complete, etc.)
But ideally, it would be a generic app not specific to Steam or games.

If you've got any ideas, thanks!