A music playout system. I put on an internet radio-like show each week and I needed a way to play music. The only solutions I could find were for Windows but my desktops are all Linux so I wrote my own.
It differs a bit from the more usual "music player". I need to know how long until the track ends and how long until it starts to fade out. I also want to add lots of comments so that I can talk about the tracks I'm playing.
Over time I've added other features - tabbed playlists, automatic lookup of titles on Wikipedia, estimated start/end times for tracks I've yet to play, ability to edit mp3 tags and - well, quite a lot more. It's just grown over time as I've needed things.
I call it MusicMuster, but I haven't actually open sourced it yet. I mean to, but imposter syndrome keeps popping up. I'll just make the code a bit better, remove that hack, etc. Maybe you know how it is.