Websites
Swami
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Soundfont editor - http://www.swamiproject.org
Musescore
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Sheet music - http://musescore.org
Calf Studio Gear
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LV2 plugins - http://calf-studio-gear.org/
Linux Studio Plugins
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LV2 plugins - http://lsp-plug.in/
Analog Modelling Synthesizer
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LV2 plugins - http://amsynth.github.io/
XSynth DSSI
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DSSI plugins - http://smbolton.com/xsynth-dssi.html
Computer Music Toolkit
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LADSPA plugins - http://www.ladspa.org/cmt/overview.html