The sort of metadata glyr is searching (and downloading) is usually the
data you see in your musicplayer. And indeed, originally it was written
to serve as internally library for a musicplayer, but has been extended
to work as a standalone program which is able to download:

* cover art;
* lyrics;
* bandphotos;
* artist biography;
* album reviews;
* tracklists of an album;
* a list of albums from a specific artist;
* tags, either related to artist, album or title relations, for example
links to wikipedia;
* similar artists;
* similar songs.