Who is The Ousters from The Rise of Endymion and what is their importance?

The Ousters are a confederation of post-humans and aliens that live solely in space, where they grow vast colonies, which are constructed of living space trees. Ousters are the descendants of humans, who were sent on deep space seedships and discovered that the only way to survive the many hostile environments into which they were sent was to incorporate nanotechnology and genetic engineering into their race. The Ousters are seen as the future of humanity.