Beast is a powerful music composition and modular synthesis application. It offers multiple input methods like multitrack, piano roll, and pattern editing and supports skins. On the technical side, it has a wide range of abilities like sequencing, unlimited undo/redo history, real-time synthesis with multiprocessor support, full duplex 32-bit audio rendering, precise timing down to sample granularity, on demand loading of partial wave files, on the fly decoding of various sample formats, aliasing free oscillators, and full Scheme scripting support.
jMusic provides a library of classes for generating and manipulating music, and is a solid framework for computer assisted composition in Java. jMusic supports composers by providing a music data structure based upon note/sound events, and methods for working with that musical data. jMusic can read and write MIDI files, audio files, and its own .jm files. jMusic is designed to be extendible, encouraging you to build upon the functionality of jMusic by programming in Java to create your own music composition tools.
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. Complete C source code and precompiled executables for Windows and Linux are provided.
libmidixx is a C++ library to manipulate MIDI sequences. It is intended for a multimedia application that handles playback, recording, and editing of MIDI sequences, though the current version just implements playback only. libmidixx supports OSS, ALSA, and serial (tty) MIDI ports, and also comes with a user-space sequencer implementation, which does a fair job on a lightly-loaded machine.
Melys is a MIDI sequencer application for ALSA. It records, plays back, and saves to a MIDI file or to an XML-based format. There is a track view where you can arrange parts using drag-and-drop and a piano-roll view where the same can be done with notes. There is also a graphical tempo view where the tempo of the song can be changed. Multiple files can be open at once, and notes can be dragged between them. It is written in C and uses the GNOME/Gtk+ widget sets.
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.
Mup produces very high quality PostScript printed music or a MIDI file from a text input file. It can handle almost any kind of music, instrumental or vocal, including tablature, shaped notes, guitar grids, alternate tunings, user-defined symbols, and much more. Mup has been under active development since 1992.