The Reality Bomb activates...
The Reality Bomb was a failure of a plan by Davros, the creator of the Daleks, to destroy everything in existance apart from the Daleks, thus leaving them to control the universe. Which was empty. And Lonely.
It would have vaporised everything in the whole universe using a twisted form of atomic control. It would have negated the intermolecular forces of each individual atom, thus vaoprising solid objects and reducing the universe to dust.
Even the Daleks knew how bad this plan was, and they were right to think so - not only was it a failure of a plan, but all the Doctor needed to do to stop them was rewrite the Bomb's software so it vaporised its housing - the Dalek Mothership. And since the Daleks had issued an order for all Dalek ships to return to the Mothership to shelter from the Reality Bomb's fire, this little tweak effectively wiped out the Dalek race. They were convinced to go through with the plan by Dalek Caan, who was actually an insane prophet of Dialga who seeked to do his bidding by destroying the Imperial Daleks, thus stopping their meddling with time.
It is interesting to note that the Reality Bomb's methodology closely resembles that of the Composer or even a Halo RIng. However, like all the Dalek Weaponry, this particular example is strictly Dalek-made.