Mono framework to create extensible applications

https://www.mono-project.com/Mono.Addins

VisualBasic.NET support for Mono

http://www.mono-project.com/VisualBasic.NET

Open source implementation of .NET Development Framework

https://www.mono-project.com/

Open source implementation of .NET Development Framework

https://www.mono-project.com/

Coding font with alternates, ligatures and contextual positioning

https://larsenwork.com/monoid

Monospace font

http://bok.net/MonteCarlo/

Sans-serif font inspired by the street signs of Montserrat

https://github.com/JulietaUla/Montserrat/

Drive a buggy across the moons surface

http://www.seehuhn.de/comp/moon-buggy

Open source MQTT broker

https://mosquitto.org/

Full-featured gopher server without dependencies

https://sourceforge.net/projects/motsognir/

Alphabet of geometric symbols based on 7x7 units

https://velvetyne.fr/fonts/mourier/

Display the current time using the X root cursor

Simple text editor for the Xfce Desktop

http://goodies.xfce.org/projects/applications/mousepad

Collection of open source fonts

http://www.theleagueofmoveabletype.com/

High-performance video filters for the GPU

https://movit.sesse.net

Improved JPEG encoder by Mozilla

https://github.com/mozilla/mozjpeg

PostScript printing util for ASCII files, email, USENET news articles, etc

Configurable tool to check collections of audio files

https://erislabs.net/ianb/projects/mp3lint/

Library and tools to read, create, and modify mp4 files

http://code.google.com/p/mp4v2/

External MIME packer/unpacker

Library of complex numbers with arbitrarily high precision

http://www.multiprecision.org/

MPD client for GNUstep

http://www.musicpd.org/MPDCon.shtml

C/C++ arbitrary precision decimal floating point libraries

https://www.bytereef.org/mpdecimal/index.html

MPEG-2 Encoder and Decoder

http://www.mpeg.org/MPEG/video/mssg-free-mpeg-software.html

Library for multiple-precision floating-point computations

http://www.mpfr.org/

Command-line player for MPEG layer 1, 2 and 3 audio

http://www.mpg123.de/

Portable implementation of MPI-1, MPI-2 and MPI-3

https://www.mpich.org/

Multiprecision integer, rational, floating point numbers library

https://github.com/wbhart/mpir/

High performance media player supporting many formats

http://www.mplayerhq.hu/

Skins for MPlayer's Graphical User Interface (GUI)

http://www.mplayerhq.hu/

Graphical Package Manager for MidnightBSD

https://github.com/laffer1/mport-manager

Free and open-source general-purpose video player

https://mpv.io

Build platform for .NET and Visual Studio

https://github.com/Microsoft/msbuild

Efficient binary serialization, like JSON but smaller and faster

https://msgpack.org/

SMTP plugin for MUAs

http://msmtp.sourceforge.net/

A collection of tools for manipulating MSDOS files

http://www.gnu.org/software/mtools/intro.html

MTP device filesystem

https://www.adebenham.com/mtpfs/

Traceroute and ping in a single network diagnostic tool

https://www.bitwizard.nl/mtr/

Traceroute and ping in a single network diagnostic tool

https://www.bitwizard.nl/mtr/

Compositing window manager forked from Mutter for use with Cinnamon

http://cinnamon.linuxmint.com/

Authentication service for creating and validating credentials

https://dun.github.io/munge/

Common components between a munin node and server

http://munin-monitoring.org/

Contributed plugins and other for munin

https://github.com/munin-monitoring/contrib

Collector part of Munin

http://munin-monitoring.org/

Node-specific part of Munin

http://munin-monitoring.org/

Build system compatible with meson

https://muon.build/

Mathematical expressions parser library written in C++

https://beltoforion.de/en/muparser/

Lightweight PDF viewer and toolkit

https://www.mupdf.com/

Decoder, encoder, and replaygain for musepack (mpc)

https://www.musepack.net/

Free music composition & notation software

https://musescore.org/ https://github.com/musescore/MuseScore