The Rehabilitator was a device to change people into more idealised forms.
The Rehabilitator looked much like a large kaleidoscope. One person would look at another person and the target would start to turn into what the other person wanted them to be like. This caused both mental and physical changes. The longer the rehabilitator was used, the longer the effect would last and the stronger the effect would be. After several hours, it would be permanent.
The Rehabilitator had side effects. Usage would cause weakness and hunger, particularly a hunger for chocolate. The alloys that made up the Rehabilitator produced radiation with an addictive effect. This addiction could be prevented with specially made viewing boxes. (PROSE: Kaleidoscope)
The Rehabilitators were created by an ancient alien race who tried to maintain peace. They were discovered by a humanoid race, who used them in their prisons. This practice was discontinued when terrorist groups got hold of three and were able to use them to convert others to their cause. After this, many Rehabilitators were scattered throughout the Galaxy.
In 2009, another Rehabilitator was found in Cardiff. Though Torchwood was able to find it, it was stolen by local kids. When they were unable to find a use for it, they gave it to Danny Dillard. He used it to try to improve his father, eventually becoming addicted to it. Though Torchwood was able to get back the Rehabilitator and remove Danny's memories, the addiction remained and Danny turned to drugs to try to recapture the feeling. (PROSE: Kaleidoscope)