Intellijel Designs Stomp

This module alows you to connect your guitar pedals into the eurorack system, it even lets you modulate the exp circuit in your pedals either by the modules own LFO or by any other modulation source in your rack.
You can even plug your guitar into it and make your rack serve as a effects unit. Suffice it to say that this little module opens up a whole new world of sonic possibilities. This module couldn't be better.