MPD is designed around a client/server architecture, where the clients and server (MPD is the server) interact over a network. Thus, running MPD is only half of the equation. To use MPD, you need to install a MPD client (aka MPD interface).
This is an (incomplete) list of free and open source MPD clients.
mpc - a solid, lightweight, simple mpd client, written in C.
ncmpc - A curses client written in C++.
ncmpcpp - A curses client written in C++ tailored after ncmpc.
pms - A console client written in Go with vi-like interface.
vimpc - A curses client with vi-like key bindings.
pimpd2 - Feature-packed cli client with interactive shell and regex queries.
nncmpp - A hybrid curses/X11 client inspired by Sonata.
mmtc - A minimal mpd terminal client
mpq - A minimal client that focuses on the mpd queue
MPD_sima - A non-interactive autoqueue client. It will queue new tracks following last.fm similar artists suggestions.
mpd-ynca - A non-interactive client to control Yamaha AV receivers with YNCA (network control) support.
bmp - Best music parts tracker for MPD
netjukebox the flexible media share - netjukebox is a web-based media jukebox for MPD, VideoLAN and Winamp/httpQ.
MPD.FM - A mobile-ready web client focussed on playing internet radio stations
PiFi Radio - A minimalist web client to listen to radio (archived).
RompЯ - A mobile-ready and desktop web client
cyp - A responsive web client based on ws2mpd with Youtube-dl integration
ympd - a web GUI written in C, using websockets and bootstrap.js
myMPD - An evolution of ympd, with minimal resource usage and dynamic playlist integration
ampd - A modern and mobile-friendly web UI using Spring Boot, Angular and websockets.
audioloader - A responsive web client with special focus on listening full albums.
cryMPD - Completed MPD Web client based on Crystal.
CoverGrid - A client for the Music Player Daemon (MPD), focusing on albums instead of single tracks
MPDCtrl - A client app for Windows desktop.
mpdevil - A small GTK+ MPD client written in python
Persephone - A modern, native client for macOS
Quimup - QUIMUP is a client for the music player daemon (MPD) written in C++ and QT3 with focus on mouse handling and drag and drop.
Skympc - Yet another QT(5) Client
Stylophone - A native client for Windows and Xbox; Also available on iOS!
Xfce4-mpc-plugin - Plugin for Xfce4 Panel
Xfmpc - A graphical GTK+ MPD client focusing on low footprint
Ymuse - Easy, functional, and snappy GTK client for Music Player Daemon (MPD) written in Go.
M.A.L.P. - A mpd client for Android
MPDroid - A modern MPD Client for Android
MPC Wear - A MPD Client for Wear OS
MaximumMPD - A MPD client for iOS
Shinobu - Modern and native client for iOS (iPhone / iPad)
Stylophone - A modern, native client for iOS/iPadOS; Also available on Windows!
mpdscribble - Last.fm scrobbler
alexa-mpd-skill - A simple Alexa skill for controlling MPD
ario - Another GTK based client.
Cantata - A Qt client.
gmpc(Gnome Music Player Client) - A fully featured client.
QMPDClient - Qt4 based mpd client, originally developed by Håvard Tautra Knutsen. Set of patches developed by community was then called “QMPDClient-ne”. Now it became mainline
Sonata - Client, now ported to Gtk3. At the writing time - more recent, compared to some other gtk clients.
There are many more clients. Please help and add them to this list.