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.
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.
Twibright Syntring is a purely algorithmic string synthesizer with ASCII tab input and wav output. It doesn't use any samples, yet sounds quite realistic. Timbre, volume, and timing are adjustable in the tab file. It can be used for learning or practicing guitar or bass playing, for editing and synthesizing one's own tunes, or producing MIDI sound fonts. It is very lightweight and portable, and doesn't require any libraries.
Algoscore is a graphical environment for algorithmic composition, where music is constructed directly in an interactive graphical score. The result is output to MIDI and CSound. Graphical objects are placed in a timeline and connected together. Some objects are fully dependent on user data, while some are generative and reacts on input from other objects. It is highly customizable and extensible with the Nasal scripting language. It has a non-realtime perspective where the composer can relate freely to time and construct the composition outside of time. This makes AlgoScore more like a traditional sequencer in this regard, but a graphical algorithmic sequencer with powerful and flexible scripting capabilities.
PianoBooster is a program that teaches you how to play the piano as well as the basics of reading musical notation. PianoBooster can play any MIDI files, listens and reacts to what you are playing on a MIDI keyboard. It makes sight reading music fun. It can make use of the "light keyboard" or "guide lamp" feature found in some keyboards, such as Yamaha EZ-200, Casio LK 220, LK-300 TV, and LK-43. Keyboards with this feature can cause specific keys to glow. PianoBooster can use this feature to show beginners which keys to press at any given time, even if they can't read musical notation.