Xtracycle isn't just another bicycle company. It's a labor of love devoted to the evolution of simple, versatile, and sustainable transportation. After 15 years of development in locales like Nicaragua, Kenya, and Stanford University's engineering labs... Xtracycle's LongTail innovation is a hitchless trailer that evolves the bike rack, bike bag (pannier or basket), bike trailer, passenger seat, and baby seat into one cargo utility bicycle system.With so many bikes already out there you can be ultra sustainable by converting your existing bicycle into a cargo bike with Xtracycle's LongTail Kit. Their website walks you through the steps - basically add the frame extension to your rear drop out and hub which extends your wheelbase by 15".
Btw, if in Portland and looking to test one out, River City Bicycles carries them and the guys there were really friendly and helpful.
All photos via Xtracycle