If you're looking a free and minimalistic music player, there's no need to continue searching because you're not going to find anything better than MusikCube. We're talking about a program under the open-source principle, therefore, you can use it freely and without paying a cent. And with regard to the design... can there be anything more minimalistic than a design based on a command terminal?
The most minimalistic audio player
This player is both a music player and a library from where we can access all our songs and server to listen to audio via streaming. This is the Windows version but there also developments for macOS, Linux, and Raspberry Pi.
Therefore, we're talking about a simple player with very basic menu navigation that allows us to explore our entire music collection really intuitively. Its configuration allows us to access all our music files and listen to those songs via streaming.
In terms of design, downloading it for Windows (or Mac) is more a fancy o eccentricity rather than a real need... there are alternatives that are much more functional right now.