The calf plugins provide 8 audio effect and 2 synthesizers. They come with many
faces. Whether you prefer ladspa, lv2, dssi or jack plugins all of this is
supported. What I like most is that the package comes with a nice tool called
calfjackhost. This gets you started immediately, just add the plugins and route them in e.g. qjackctrl. All plugins have nice control UIs. Some of the UIs are
much fancier what one is used to in the Linux world. Take the "multi chorous" as
an example. Beside the usual control knob it should live animated displays of
frequency response and LFOs. Most plugins come with a bunch of presets to demo
the wide range of sounds they can produce.
Verdict: Definitely worth installing for Linux audio musicians.