Singularity scalpel

The Singularity Scalpel was an alien medical device, believed to be used for operating on a body without surgery. It was discovered by Torchwood Three, but they were unable to use it properly at first. When they tried to remove a Mayfly from a Billy Davis, they accidentally killed him, blowing open his stomach. After practice, Owen Harper managed to use it to kill a Mayfly which had been implanted into Martha Jones. (TW: Reset)

Owen took it to Gwen Cooper's wedding as he planned to use it remove the Nostrovite egg from her. He had modified it for this purpose. Owen gave it to Rhys Williams and showed him how to use it (Owen being uncomfortable with his own ability to do so due to his permanently broken right hand). With this knowledge, Rhys managed to remove the egg without killing Gwen. (TW: Something Borrowed)

Jack Harkness used it to kill the Vam after weakening its molecular structure with sonic cannons. He set it on a wide band, causing the Vam to explode, coating much of Cardiff in oil. (TWN: Risk Assessment)