A matter converter is a piece of Asgard technology capable of using stored information patterns to create a device out of matter.
In the 2006 of an alternate timeline, Lt. Colonel Samantha Carter discovered that she could tweak the Asgard transporter on the Odyssey using information from the Asgard computer core to act as a matter converter, synthesizing necessities for the fifty to sixty years SG-1 and General Hank Landry were trapped aboard the ship. Amongst these were oxygen, food and tretonin for Teal'c. (SG1: "Unending")
Later in 2007, the now-Colonel Carter gained control of the matter converter of the Aegis. Using the records of the matter patterns of the First Atlantis Reconnaissance Team's gear when Fenrir beamed the team off the ship, Carter is able to synthesize two radios, two G36Ks and an FN P90 Personal Defense Weapon for the Tau'ri's use. After gaining control over the main matter converter platform in the Aegis computer core, the Wraith are able to use the designs stored within the ship's mainframe to synthesize the deadly isa device. (SGA: "Nightfall")