[Ezhik]

For Windows users, there's mpv.net, which adds a GUI for configuration editing and a command palette. [1][2]

There is also mpc-qt, which replicates the classic MPC-HT UI, but with libmpv as the backend. [3]

Personally I found mpv's defaults sane enough to not need a GUI for it, but I did release an unofficial version to the Windows 10 Store with a wrapper that adds file association and macOS-style single instance support. [4][5]

[1] https://github.com/stax76/mpv.net

[2] https://www.microsoft.com/store/productId/9N64SQZTB3LM

[3] https://github.com/mpc-qt/mpc-qt

[4] https://github.com/SilverEzhik/mpv-msix

[5] https://www.microsoft.com/store/productId/9P3JFR0CLLL6

[thrdbndndn]

I use SMPlayer. Despite somewhat "ugly" UI, it's a very capable MPV skin.

[1] https://www.smplayer.info/

[RGamma]

SMPlayer is a GUI for the (quite old now) MPlayer.

IIRC a long time ago mpv was based on mplayer, though probably no shared code exists anymore.

[thrdbndndn]

No, you can choose to use MPV or Mplayer. The default is MPV too IIRC (on Windows, as the parent comment mentioned).