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.
Minnow is a concurrent programming language with a Ruby-like syntax. It compiles to an executable and uses a companion library to allow fully-rebalanced microthreads. Minnow gains a lot of strength from its actor model, which uses message passing, as opposed to threads and locking, as its concurrency model. Taking a cue from Erlang, actor creation and message passing is extremely lightweight (often on the order of a few nanoseconds). The language has a built-in foreign function interface that allows developers to leverage existing C-based libraries in a simple SWIG-like manner. Minnow's object model is based on "melding" features together to form objects.
DromeAudio is a small audio manipulation and playback library. It features a simple API for loading, generating, processing, and playing audio. Some of its features include loading and saving WAV sounds, loading Ogg Vorbis sounds, audio mixing/playback, and dynamic audio processing effects such as pitch shifting and echo.
Factor is a dynamically-typed stack-based programming language. Factor runs on various OSes and CPU architectures, and provides an optimizing compiler, interactive development environment, powerful collections, higher order programming, continuations, and a growing library of contributed code.