DeaDBeeF (as in 0xDEADBEEF) is a modular cross-platform audio player which runs on GNU/Linux distributions, macOS, Windows, *BSD, OpenSolaris, and other UNIX-like systems.
DeaDBeeF plays a variety of audio formats, converts between them, lets you customize the UI in almost any way you want, and use many additional plugins which can extend it even more.
* The screenshot above demonstrates a highly customized DeaDBeeF, running on Linux with several additional plugins