Mission First Tactical is making a 7″ aluminum quad-rail for the AR-15.  Called the T-MARC (Tekko Metal AR Carbine) Integrated Rail System, it replaces the standard handguard with a unit that has four Picatinny rails.

No screws or gunsmithing is needed to install this quad rail, rather it is held in place by a ring and cap.  The rail system is made of 6061 aluminum in the United States.  It is hard coat anodized and comes with a lifetime warranty.  MSRP is $124.99.