rakarrack is a decent effects rack for linux. It's not packaged for ubuntu(of course), but is fairly easy to compile. I've been using the cvs version (yes, people are still quite happily using cvs it seems). Once you get it set up you have access to 80 presets of realtime guitar effects(2-40ms depending on your computer sound card setup). It works with the jack audio system, so you can route audio into it, and route its audio out to other programs easily enough. You can also control it with midi(alsa, or jack). Meaning you can hook it up to a midi controller of some sort. I've been using it with an maudio axiom 25 controller, and with python scripts via pygame.midi. It even has a very nice help manual integrated into the program... I wish more programs had a good help section. It details the 17 different effects that come with the program. One thing which is a bit funny is that it doesn't use LADSPA or lv2 plugins. You can of course still use these other plugi...