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.
Lyra is a front-end to the Music Player Daemon (MPD). Based loosely on the Creative Media Source software, it has the aim of supporting large collections of albums and artists. Other interesting features are the implementation of a local cache of the music library using an SQLite database, increased speed, and flexibility. In addition, Lyra supports integration with the Last.fm service, which includes "Scrobbling" and album cover art.
Esdl is library for accessing SDL and OpenGL through Erlang. SDL handles 2d graphics, user events, and audio while OpenGL handles 3d graphics. SDL (Simple DirectMedia Layer) is a cross-platform multimedia library designed to provide fast access to the graphics framebuffer and audio device. It also does event handling from mouse, keyboards, and joysticks. OpenGL is a cross-platform standard for 3D rendering and 3D hardware acceleration.
MrsWatson is a commandline audio plugin host. It takes one or more plugins, sends an audio signal to them for processing, and saves the resulting output. Although the plugins think they are running in realtime, processing is actually done offline (this is not the same as the "offline" processing in VST terminology). This makes MrsWatson ideal for developing or debugging plugins, or processing audio on a server.
Sfront compiles MPEG 4 Structured Audio (MP4-SA) programs into efficient C programs that generate audio when executed. MP4-SA is a standard for normative algorithmic sound, which combines an audio signal processing language (SAOL) with score languages (MIDI and SASL). Under Mac OS X and Linux, sfront supports real-time, low-latency audio input/output and MIDI input. Under Mac OS X, sfront supports the creation of AudioUnit plug-ins. The documentation includes a book about SAOL programming.