Interest in Linux based MIDI is growing and this list will probably not reflect the true amount of MIDI software available, but should provide a reasonable selection of applications.
If you are developing, or know of, any other MIDI apps not listed here please drop me a note.
The Advanced Linux Sound Architecture is composed of several parts. The first is a fully modularized sound driver which supports module autoloading, devfs, isapnp autoconfiguration, and gives complete access to analog audio, digital audio, control, mixer, synthesizer, DSP, MIDI, and timer components of audio hardware. It also includes a fully-featured kernel-level sequencer, a full compatibility layer for OSS/Free applications, an object-oriented C library which covers and enhances the ALSA kernel driver functionality for applications (client/server, plugins, PCM sharing/multiplexing, PCM metering, etc.), an interactive configuration program for the driver, and some simple utilities for basic management.
OSS provides sound card drivers for most popular sound cards under Linux and FreeBSD. These drivers support digital audio, MIDI, synthesizers, and mixers found on sound cards. These sound drivers comply with the Open Sound System API specification. OSS provides a user-friendly GUI which makes the installation of sound drivers and configuration of sound cards very simple. It supports over 200 brand name sound cards, and provides automatic sound card detection, Plug-n-Play support, support for PCI audio soundcards, and support for full duplex audio.
Notemidi is a device driver for MIDI output via the RS-232 serial port on notebook/laptop computers. Notemidi can be used with the MIDIator MS-124W interface, Roland Sound Canvas sound modules, or Yamaha MU-x series sound modules.
http://www.michaelminn.com/linux/notemidi
KMid is an X11 / KDE based midi player for Linux and FreeBSD. It displays the text of karaoke files and changes its colour as it is being played so that the tune can be easily followed. KMid uses /dev/sequencer as output device supporting external synths, AWE , FM and GUS cards.
http://perso.wanadoo.es/antlarr/kmid.html
Pmidi is a straightforward command line program to play Midi files through the ALSA sequencer.
http://www.parabola.demon.co.uk/alsa/pmidi.html
TiMidity is a MIDI to WAVE converter that uses Gravis Ultrasound(*)-compatible patch files to generate digital audio data from General MIDI files. The audio data can be played through any sound device or stored on disk. On a fast machine, music can be played in real time.
http://www.goice.co.jp/member/mo/timidity/
Brahms is a sequencer and music notation program with several editing methods so far including Score-, Pianoroll-, Drum-, and Mastertrack Editors. For C++ programmers, it is easy to implement further editors by deriving from a general editor-class. MIDI Import and Export is also implemented. In combination with aRts-0.3.4, one can play wave-files and make use of the midibus to send midi-events to the software synthesizer.
Formerly known as KooBase
http://brahms.sourceforge.net/
Anthem is an advanced open source MIDI sequencer. Anthem allows you to record, edit and playback music using a sophisticated and acclaimed object oriented song technology.
http://anthem.sourceforge.net/
JAZZ++ is a full featured, audio capable midi sequencer for Linux and Windows.
http://www.jazzware.com/cgi-bin/Zope.cgi/jazzware/
UltiMusE-LX (the Ultimate Music Editor) is a composing program. No, it doesn't compose for you; it's a "word processor" for music. You draw sheet music on the screen using the mouse and/or computer keyboard. Up to 16 parts or voices fit on up to seven staves (staffs). Most standard musical notations are supported, as are MIDI instrument patch changes, events, and real-time clocks.
http://hometown.aol.com/knudsenmj/myhomepage/umuselx.htm
Melys is a Midi sequencer application for the Advanced Linux Sound Architecture (ALSA). Melys uses the sequencer support of ALSA, along with the GNOME libraries to produce a powerful and easy to use sequencer.
http://www.parabola.demon.co.uk/melys/
MidiMountain is a sequencer to edit standard MIDI files. Its easy-to-use interface should help beginners to edit and create MIDI songs (sequences), and it is designed to edit every definition known to standard MIDI files and the MIDI transfer protocol, from easy piano roll editing to changing binary system exclusive messages.
MusE is a Qt 2.1-based MIDI sequencer for Linux with editing and recording capabilities. While the sequencer is playing you can edit events in realtime with the pianoroll editor or the score editor. Recorded MIDI events can be grouped as parts and arranged in the arrange editor.
Rosegarden is an integrated MIDI sequencer and musical notation editor.
http://www.all-day-breakfast.com/rosegarden/
ttrk (tektracker) is a console MIDI sequencer with a tracker-style step editor. It is built for live playing, with convenient track mute buttons and loop control. ttrk supports both sending and syncing to MIDI clock pulses.
ShakeTracker aims to be a fully-featured MIDI sequencer with a tracker interface. It currently works well and supports most tracker effects. Anyone who has used Impulse Tracker before will feel at home, and for the new users, a simple but extensive help system is provided. Most commands and shortcuts resemble their tracker counterparts.
http://reduz.com.ar/shaketracker/
DrumPatterns is a free, open source, web oriented drum patterns generator, whose purpose is to help teach drum patterns. It can teach the rudiments as well as advanced rhythms. It can output characters, score, or Midi, and includes hours of samples.
http://www.linux-france.org/prj/drumpatterns/index-en.html
JSynthLib is an Open Source Universal Synthesizer Patch Editor / Librarian written in the Java Language. The project aims to eventually provide support for all existing Synthesizers by providing methods and documentation which allow users to develop drivers and editors for unsupported synths and contribute them to the project.
Spiral Synth is a physically modeled polyphonic analogue synthesizer. It is capable of creating the kind of sounds made by hardware analogue synths, the noises used in electronic music. You can also use it to make stranger sounds too. MIDI is supported, and it uses the standard OSS/Free sound output (/dev/dsp).
http://www.pawfal.org/SpiralSynth/
UltraMaster Juno-6 is a faithful virtual reproduction of a Roland Juno-6 Polyphonic Synthesizer. It features realtime 64-bit internal ULTRANALOG wave synthesis, an early 80's style arpeggiator and chorus, and 100s of patches to save your own custom settings. All parameters can be controlled in realtime, via on-screen GUI or external MIDI controllers.
http://www.ultramaster.com/juno6/index.html
"Pd" stands for "pure data". Pd is a real-time software system for live musical and multimedia performances. It is in active development by Miller Puckette , and perhaps others. The system is unfinished, but quite useable for sophisticated projects. It has been ported to Linux, IRIX, and many flavors of Windows.
Csound is a software synthesis program. But more than that, Csound doesn't suffer the same kinds of limitations that other software & hardware synthesizers have. There are no limits to the amount of oscillators or filters one can use. Csound is also completely modular, so that any function in Csound can be used in an array of ways.
Bristol is a synthesizer emulation package. It includes a Moog Mini, Moog Voyager, Hammond B3, Prophet 5, Juno 6, DX 7, and others.
http://www.slabexchange.org/index.cgi?DOWNLOAD
Adds midi file support for x11amp (via timidity). A crude mixer interface is provided via the configuration dialog.
http://ban.joh.cam.ac.uk/~cr212/xmms-midi/
Mup takes a text file as input and produces PostScript output for printed music. It can handle both regular notation and tablature notation. (It can also produce MIDI output.)
LilyPond is a music typesetter. It produces beautiful sheet music using a high level description file as input. LilyPond is part of the GNU Project.
Sfront compiles MPEG 4 Structured Audio (MP4-SA) bitstreams into efficient C programs that generate audio when executed. MP4-SA is a standard for normative algorithmic sound, that combines an audio signal processing language (SAOL) with score languages (SASL, and the legacy MIDI File Format). Under Linux, sfront supports real-time, low-latency audio input/output, local MIDI input from soundcards, and networked MIDI input using RTP and SIP. A SIP server hosted on the Berkeley campus manages sessions. The website includes an online book about MP4-SA.
http://www.cs.berkeley.edu/~lazzaro/sa/index.html
jMax allows one to interactively design dataflow circuits. The basic data types that can go through are integers, symbols, lists, etc. It is an event-driven system and has been used for MIDI processing. A second part of the system (DSP) allows a continuous signal to flow through a circuit, which is most useful for PCM sound (ie. microphone, sound files, etc). The system is extensible by using shared libraries, you may add data processor types, data types, GUI elements, device types, and more. Data processors may also be designed as circuits and reused.
http://www.ircam.fr/equipes/temps-reel/jmax/
TSE3 is a powerful open source sequencer engine written in C++. It is a 'sequencer engine' because it provides the actual driving force elements of a sequencer but provides no form of user interface. Sequencer applications or multimedia presentation packages will incorporate the TSE3 libraries to provide a user with MIDI sequencing facilities.
KeyKit is a multi-tasking interpreted programming language (inspired by awk) designed exclusively for realtime and algorithmic MIDI manipulation. KeyKit's GUI provides several dozen tools for algorithmic music experimentation, including a multi-track sequencer and drum pattern editor. The GUI and all tools are completely written in the KeyKit language itself. This allows users to add new tools and operations to the existing tools, even while the system is running.