Nanotech weapons archive/assembler.
A relative of the Encyclopaedia Everythingiana or the more capable (or limited depending on one's point of view) Santa Claus/Genie machines: the warchive is an assembler complex equipped with an AI of sufficient capability to design and build anything you ask for (given the restrictions and personal inclinations of the AI).
A standard warchive includes a virtual interface, computronium data storage banks holding the templates for literally trillions of weapons - everything from a crude stone axe to a man-portable tandem plasma cannon/fractal gauss gun/amat rifle - and a wide spectrum nanofab unit. The user inputs the choices and usually waits about an hour for the gun to assemble.
Amat weapons require the user to acquire the amat separately, although the more advanced warchives come with their own amat supplies.