Okay, before you can make a "gravitic weapon", you have to understand the nature of Gravity -- and then the nature of the Sci-Fi "Technobabble" that's been associated with Gravity.
So, what is Gravity? That's simple, we all know that. Gravity is a "force" (I won't go into just what kind of force, now) which "attracts"; that is, it pulls things towards the source of gravity. It PULLS.
Okay, that's Gravity. Now, the next step is to define "Gravitic Technology". What is "Gravitic Technology". Well, as I see it, there are three basic Grav Technologies. The first, and most basic Grav Technology is Anti-Gravity. You should think of Anti-Gravity technology as Gravity Shielding -- that is, it "shields" you from Gravity.
A really bad analogy for this effect is an umbrella in a rainstorm. If you think of the force of Gravity as the rain (which is a bad analogy, because rain "falls", while gravity "pulls"), but anyway, if you think of the force of Gravity as the Rain, then the Umbrella is the Anti-Gravity effect. The bigger the umbrella, the drier you get = the stronger the Anti-Gravity shield, the less hold Gravity has on you. Another, slightly better, analogy is that of the Helium Baloon....Gravity is pulling you "down". A really weak AG shield would be like grabbing 1 helium-filled baloon. The stronger the AG shield gets, the more helium baloons you are holding.
Thus, the Anti-Gravity Effect works to reduce the Apparent Weight of items inside the field. It doesn't "push", it doesn't "pull", it just negates the affect of the existing gravity in the area. Anti-Gravity technologies would be limited to those technologies that have to do with Lifting -- AG Backpacks, AG Cargo Pallets, AG Beds. These items would be set for Percentage of Local Gravity Nullified. Thus, the AG Backpack, set at 50% Nullification, would make the contents "appear" to "weigh" half as much as they really do. As far as an Anti-Gravity weapon...the only one I can think of is an AG Landmine. Set for 100% Nullification, once tripped/activated everything inside the area of effect would suddenly become COMPLETELY shielded from the effects of the planet's gravity. Out in space this would mean nothing, but on the surface of a planet, suddenly losing the pull of gravity meant that anything inside the area of effect would be affected ONLY by the spin of the planet -- thus you would be flung into the air at the rotational speed of the planet -- with, for Earth, is, like, 25 miles per second. Imagine, you're walking along and suddenly -- pop! -- the AG Landmine activates, and you are flung up into the air at 25 mi/s. However, you are flung off at a TANGENT -- NOT straight up! So, a few seconds later, you slow down enough for gravity to once again start pulling you down -- from about a half-mile up! Can you say "Squish"?
The second Gravitic Technology that would be developed would be the artificial creation of a Gravitic Field, or Artificial Gravity. This technology SIMULATES the gravitic effect of "pulling", without the need of all that nasty old MASS. Thus, a 1 meter square of wiring and composite alloys, along with enough electrical power, can, from up to 3 meters, or so, produce the same amount of attraction towards itself -- the same amount of "pull" -- that it takes the entire PLANET to produce, through sheer bulk. Pretty impressive, actually. But, in a sci-fi world, fairly simple technology.
The most obvious device that uses this technology is Deckplating in starships and space stations. Also, flooring of buildings on low-G worlds can be similarly equipped. Entire communities on low-G worlds can be outfited this way. As for Weapons that can make use of this Technology, the most obvious is the Grav-Bomb. A small Grav Generator is designed to rapidly overload -- thus creating an intense, localized Grav Field. In otherwords, a Micro Singularity. This effect is uncontrolled, and fairly short ranged -- because the generator is destroyed within microseconds of activation. But then, so is the mechanism of a Thermonuclear bomb. The effect of a Grav-Bomb is an Implosion. For just a second, everything in the area of effect is sucked in towards the center of the Implosion -- structures suffer sudden sheer and torsion, buildings collapse, hullplating is ripped of ships, missiles (and maybe even lasers!) are pulled off-course.
A "focused" Artificial Gravity "beam" is called a Tractor Beam; but all it can do is "pull". This COULD be used offensively -- to yank folks off their feet, alter the course of objects in-flight, tear down walls, etc. -- by judicious use of a momentary "on-off" pulse of the generator. Also, a vehicle passing overhead (or in orbit) could grab a target on the ground, lift it up, then drop it from graet height. Or, a pair of Tractor Beams, working together from different vectors, could target the same object, and rip it apart with differential forces.
And finally there is Contragrav. This technology generates a gravitic "force" which, instead of "pulling" has the reverse effect -- it "pushes". This is the technology of Thrusters, and the (CT) Grav Belt. As far as weapon usage is concerned, this is also the most variable technology.
A Contragrav-Bomb would generate an expanding shockwave -- i.e., an Explosion, but without any thermal effects (no heat/flames/plasma, etc.)
A focussed Contragrav "beam" is a Repulsor. A Repulsor beam, at low levels, can be used to give objects a good hard "push" -- like people, in-coming missiles, walls, etc. At higher energy levels, the Repulsor Beam becomes a Shock Cannon (also called a Grav Lance), striking a target with pure, damaging, kinetic "force".
Also, small Repulsor generators could be used to impart high-velocity to solid objects. Thus a gravitic equivalent of the Gauss weapons is possible.
All these weapons are possible, it's just a question of application of energy, and energy efficiency.
ALL of these "gravitic weapons" would be short ranged. All the various gravitic "bombs" would have smaller areas of effect than either their conventional chemical, or nuclear, counterparts. The only difference is that gravitic bombs don't produce radiation side-effects -- of either the thermal or ionizing types. Shock Cannons are neat, but lasers have a longer range So do particle weapons. And they have less kick-back -- must remember Newton's Third! -- and, probably, use less power.
But none of this INVALIDATES the technology! I can see advantages of dropping a few Grav-Bombs rather than a few Nukes, if I have the choice. And, just like Nukes, Grav-Bombs have the advantage of smaller size over Chemical Explosives of similar power. Shock Cannon may have lower range than Lasers, but hit something with a Laser Cannon, and you just melt a hole in it -- smack something with a Shock Cannon, and you smash it back across the battlefield! Anything behind it goes Crunch!
That's just my 2 credits worth, anyway....
