Sabot Rounds Are pretty common. But its really no different then a Rail Gun. There really isnt much for "projectile" weapons that doesnt involve rocket thrust chemical or magnetic propellents. In the end you really get things that are close to the RPG and Rail Gun. The Pipe organ is just the Extreem of this. OP2 has pretty much covered the generic weapons. Lasers, Projectiles, Rockets, Lightning bolts, Magnetic weapons, Large bombs, Foams, and Acids. All you could really add but they wouldnt fit in. Flame or Plasma based throwers. ION/Partical cannons (tank mounted). Anti Weapons like ECM(Electronic Counter Measures) to cut off communitcations with tanks making them uncontrollable so they just do what ever there programed to do. Then the weapons that no one wants. Nukes.