LADSPA audio plugins, DSP utilities and investigations.
caps is the collection offering improvements over all previous efforts released here, and then some.
the pvoc collection has more LADSPA units and a time-stretching utility.
a valve-emulating preamp model, version 2.
unmatched and matched also do 'cheap' amp/cabinet emulation.
an older spiced 12AX7 analysis and a simple hard clipper.
There are RPMs of the older plugins available too, prepared by Adrian Likins: http://people.redhat.com/alikins/repo/RPMS/.
You may want to read the GPL.