yoshimi - Yoshimi is a software synthesizer for Linux based on the 2.4.
Zebralette - u-he makes creative software synthesizers and effects.
FluidSynth - FluidSynth is a real-time software synthesizer based on the SoundFont 2 specifications and has...
Piano Scribe - Open-source demo to convert audio to MIDI using a neural network.
AmazingMIDI - Free WAV to MIDI converter for music transcription.
ZynAddSubFX - ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.