The Ood are docile, psycic beings from the planet Ood Sphere. They have three brains, a brain in their head, a brain they hold in their hands and a large, singluar brain that links all the Ood together. Because they are psycic they can communicate telepathically, read minds and even see the future, but their telepathic nature allows them to be controlled by powerful minds.
They were enslaved for a short time, and were 'processed', that is, they had their hand brains cut off and replaced with translator orbs, and the singular brain was captured to make them obey. They were freed, however, by the Doctor, and were able to roam free once again.
Because of their contact with humanity their development accelerated ten-fold, and in just 3 million years they had transcended completely.