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. After practice, Owen Harper managed to use it to kill a Mayfly which had been implanted into Martha Jones. Prior to this, he killed a man when attempting to eradicate a Mayfly, but blew open his stomach instead. (TW: Reset)

Owen took it to Gwen Cooper's wedding as he planned to use it remove the Nostrovite egg within 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)