In a sense it is, but not the way it is depicted in science fiction.
One of the fundamental properties of gravity that we know of is that it is universal. What that means is that it affects everything equally, regardless of material composition. This is very important. Think: we can use electricity and magnetism because different materials react to them differently. Some are insulators, some are conductors. Some are magnetic, some aren't. Some are transparent to light (electromagnetic radiation), some are opaque. And so on. Now imagine if you had only one type of material. Imagine if everything (including the air you breathe, the water you swim in, your own body even) was made of the same material, the only difference being in density and pressure. Hard to imagine, right? Yet that's what things look like from gravity's perspective.
Which means no gravity motors, no gravity conductors, no shielding from gravity.
But what about anti-gravity? This is where another property of gravity enters the picture. Namely that it is a so-called tensor field. Why does that matter? Because in a tensor theory, like charges attract each other. So every object that has positive mass will be attracted to other objects of positive mass. There is no repulsive force. Unless...
Unless stuff exists with negative mass. But that would be Really Bad News. Because negative mass means negative energy (remember, mass and energy are equivalent.) Negative energy means less energy than the energy of empty space, i.e., the vacuum. Which means that if negative energy stuff existed, the vacuum could decay into it. It would be unstable. Indeed, we believe that this is precisely what happened in the extreme early universe, during the symmetry breaking epoch, when the negative energy of the Higgs field made the universe unstable and let it decay into its present form, endowing certain particles with mass through the Higgs mechanism and creating the form of nuclear interactions that we see today. But if such a breakdown occurred now... the universe as we know it, including all matter, including some of the seemingly fundamental laws of physics (e.g., the physics responsible for the periodic table of elements) would cease to exist. Now we don't want that, do we. So maybe it’s a Good Thing that we never observed forms of matter with negative mass-energy.
But then... why did I say that some form of anti-gravity is real? Because... in certain situations, we can create objects that effectively behave as though they had negative mass, because their mass density is less than that of the surrounding medium.
Take a bubble in the sea. What does it do? It rises. Why does it rise? Because of gravity. But that's anti-gravity! How can it happen? Well, if you wanted to be a pedant about it, you'd say that it's not the body that rises, but the surrounding water that falls. But that doesn't really tell much... especially if I had a means to create a gas with a density greater than that of water. That bubble would sink. So air bubbles rise, very simply, because they are lighter than the surrounding medium.
And in a sense, something similar happens on the largest of scales, with the accelerating expansion of the universe. The universe today is believed to be roughly 70% "dark energy". Dark energy has huge negative pressure. For a normal substance, e.g., dust or gas, self-gravity causes it to contract (that's how stars are born). Gravity does work by increasing that stuff's positive pressure. But what about stuff with negative pressure? It turns out that self-gravity works on such stuff, too... by making it expand. Kind of how a bubble rises in the sea. For the past 4-5 billion years, our universe has been dominated by dark energy, and because the effect of self-gravity on dark energy is repulsive, this caused the expansion of the universe to accelerate. This, too, is a form of anti-gravity, then.
Unfortunately, it's unlikely that any of this will ever help us create practical anti-gravity or artificial gravity machines. Too bad.
