Software synthesizer based on the SoundFont 2 specifications
FluidSynth is a real-time software synthesizer based on the SoundFont 2 specifications and has reached widespread distribution. FluidSynth itself does not have a graphical user interface, but due to its powerful API several applications utilize it and it has even found its way onto embedded systems and is used in some mobile apps.
Compresses music from 1/50th to 1/100th its original size by removing dissonant parts of sound and also optimizes it for lower speaker-stress, dynamic equalization (2-3 times less hearing stress at high volume), non-compression modes and much more.
Lightform is a complete music composition application in pre-alpha, written in python with a C backend. It's designed to have the capabilities of programs like Reaktor and Sonar, but with a simplified user interface using a python gui lib called tGUI.