The Deployable Compact Armorers Tool (D-CAT) from Space Age Weaponry fits in the storage compartment of a standard AR-15/M-16 fixed butt stock. It weighs just 6 ounces. It is the only tool necessary to assemble the AR-15/M16 from component parts, or perform a complete disassembly.
The Deployable Compact Armorers Tool (D-CAT) is available at Brownells.
Good video. I hope I never have to buy an AR-15.