Parallel cannons were powerful weapons developed by the Time Lords for use against the Enemy during the War in Heaven.
These weapons fired a point hole towards another part of the universe into the nova of an anti-sun. This allowed the neutrinos from that dimension to pass into the normal one. The tear opened like a deluge. Physics worked differently there and the neutrinos destroyed anything they encountered. Normal matter simply fell apart under the principle of quantum shattering. Organic matter lasted a fraction of a second longer before disintegrating. If a parallel beam was left on long enough, it could eat through a world in three hours and destroy its atmosphere in nine.
They were considered an antique weapon. The Third Zoners were on the verge of developing them before the end of the war in the Fifth Time Assault. Its primary advantage was that it avoided the attention of the Enemy. (PROSE: The Taking of Planet 5)