Yoshimi is a software audio synthesizer, originally forked from ZynAddSubFX.
LMMS
Let’s make music
with a free, cross-platform tool for your computer.
idrumkv1
drumkv1 is an old-school all-digital drum-kit sampler synthesizer with stereo fx.
Patroneo
An easy to use, pattern based midi sequencer, a program that sends digital “notes” to software instruments such as synthesizers and samplers.
NON
Non is the result of one man’s desire to build a complete free-software Digital Audio Workstation on GNU/Linux that really works–on accessible hardware.
Rosegarden
Rosegarden is a music composition and editing environment based around a MIDI sequencer that features a rich understanding of music notation and includes basic support for digital audio.
Inqaku leMuse
Create, play and print beautiful sheet music
Helm
Helm is a free, cross-platform, polyphonic synthesizer that runs on GNU/Linux, Mac, and Windows as a standalone program and as a LV2/VST/AU/AAX plugin.
Luppp
Luppp is a music creation tool, intended for live use. The focus is on real time processing and a fast and intuitive workflow.
ipadthv1
padthv1 is an old-school polyphonic additive synthesizer with stereo fx.