SpiralLoops is a simple visual tool for looping, layering, and warping of sounds. Sounds can be input from either wav files on disk, or from sound generating plugins. You can create loop-based compositions with the minimum feedback time between the decisions you make and your ears. The looping mechanism is very flexible, allowing you to lock the timing of loops together or to offset them for creating complex sequences such as polyrhythms.
Spiral Synth is a physically modelled 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).
SpiralSynth Modular (or SSM) is an object orientated modular softsynth / sequencer / sampler. Audio or control data can be freely passed between the plugins, and is all treated the same. Data can also be fed back on itself for chaotic effects. LADSPA plugins are supported, and you can use them in the same way as any of the native plugins. Not having MIDI won't restrict what you can do. It currently uses the standard OSS/Free sound input/output (/dev/dsp), and should work on ALSA too. You can also render WAV files directly to disk.
Fluxus is a graphical live coding environment for Scheme. Fluxus reads live audio or OSC network messages which can be used as a source of animation data for real-time performances or installations. Keyboard or mouse input can also be read for simple game development, and a physics engine is included for realtime simulations of rigid body dynamics. The built in scheme code editor runs on top of the renderer, which means you can edit the scripts while they are running.