Free / Open Source Audio Plugins:

LV2

• Calf ​http://calf.sourceforge.net/
• LL ​http://ll-plugins.nongnu.org/
• SWH ​http://plugin.org.uk/lv2/
• Zyn ​http://home.gna.org/zyn/
• Invada ​http://www.invadarecords.com/Downloads.php?ID=00000264
• IR Convolution Reverb ​http://factorial.hu/plugins/lv2/ir

LADSPA

(LADSPA plugins are no longer supported directly; however you can still use them by setting up the ​naspro ladspa to lv2 bridge. You also need to install ​slv2 from the drobilla repository for this to work correctly.)

• AMB ​http://kokkinizita.net/linuxaudio/index.html
• Blepvco ​http://www.smbolton.com/linux.html
• Blop ​http://blop.sf.net
• CAPS ​http://quitte.de/dsp/caps.html
• CMT ​http://www.ladspa.org/cmt/
• FIL ​http://kokkinizita.net/linuxaudio/index.html
• FOO ​http://www.studionumbersix.com/foo/
• MCP ​http://kokkinizita.net/linuxaudio/index.html
• NJL ​http://www.ecs.soton.ac.uk/~njl98r/code/ladspa/njl-plugins/
• Omins ​http://www.nongnu.org/om-synth/omins.html
• REV ​http://kokkinizita.net/linuxaudio/index.html
• SWH ​http://plugin.org.uk/
• TAP ​http://tap-plugins.sourceforge.net/
• VCF ​http://www.suse.de/~mana/ladspa.html
• VCO ​http://kokkinizita.net/linuxaudio/index.html
• VLevel ​http://vlevel.sourceforge.net/
• Vocoder ​http://www.sirlab.de/linux/download_vocoder.html
• WASP ​http://linux01.gwdg.de/~nlissne/wasp/index.html (maintainer wanted!)
• Nova ​https://tim.klingt.org/nova/download/nova_filters-0.2.tar.bz2

Outdated/Broken?

• Clipper ​http://quitte.de/dsp/spiced-12AX7.html
• Lemux ​http://lumatec.be/joost/
• Preamp ​http://quitte.de/dsp/preamp.html
• PVOC ​http://quitte.de/dsp/pvoc.html
• Unmatched ​http://quitte.de/dsp/unmatched.html
• Q2Ladspa ​ftp://mustec.bgsu.edu/pub/linux/q2ladspa.tar.gz

DSSI

• Examples ​http://dssi.sf.net
• Lars' Plugins ​http://ll-plugins.sf.net
• WhySynth ​http://home.jps.net/~musound/whysynth.html
• X-Y Controller ​http://www.skynet.ie/~jmmcd/software/xy-controller-dssi.tar.gz