There are a couple different solutions, depending on where you have your music.

For organizing, as another user suggested, Picard is your friend. You point it to your collection and can have it move and correct file tags all in one go. It even has default naming scripts for folders so it will go [Album Artist]->[Album], and if that doesn't suit your fancy you can edit the script however you'd like.

If where you store the music is all local (on your machine), then there are hundreds of great local players depending on platform that you can just point towards your music collection and shuffle. I have a massive collection myself that I will usually browse through randomly ordered albums until something catches my eye.

If you're looking to stream it to your own devices, then you're looking at something like a subsonic compatible server will offer a wide variety of options and platforms for playback. I go through some of this in more detail in a blog post as well, with some specifics https://illegal.solutions/posts/streaming_sucks.

If you keep each album in its own folder, basically any app will be able to use the MP3 tags to keep things organized for you. Really even the folders aren't needed, you could just have a huge directory full of every MP3, but that would be annoying to deal with for other reasons.

Something like https://picard.musicbrainz.org/ can be used if you want to get more complicated. For instance I like to keep albums in folders per release year.

> Do you have any recommendations for casual listening of downloaded music files?

Other than the simple approach of playlists and/or shuffle, unfortunately no.

> I just want an easy way to put some music on while I'm working.

Think of Bandcamp as a record store, not a radio station.

You open the music you download with something like IINA or Doppler, and you're off to the races. What exactly is the hurdle?

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