The main problem you're going to run into is that complete control of these forces would be, to put it bluntly, mad overpowered. Being able to control any of the forces, even the weak force, would make you a god of destruction. You said "no planet destroying abilities", which in my opinion is simply incongruous with having powers over these forces, any of which have the power to destroy the universe as we know it. However, I'll do my best to stick to more relatively mundane applications.
Disclaimer: I am a biologist and a programmer, well, actually a student studying to be those things, so physics in not my area of expertise. Feel free to correct me if any of the science below is downright inaccurate, but also keep in mind I'm intentionally simplifying and not concerned with using the most correct language possible.
Notice: this answer has been edited substantially since it was posted, with major rewrites of the sections regard Gravity and the Strong Force.
Gravity is unique among the forces in that it is best described not by quantum mechanics but by general relativity, via the curvature of spacetime. So one interpretation of gravity-based powers would be power over spacetime itself: wormholes, time travel, banishing people into pocket dimensions, etc. However, I’m going to focus on a more conservative interpretation and define gravity-based powers to mean the ability to affect the acceleration experienced by massive objects in a gravitational field.
Gravity is by far the weakest of the four forces. You basically need planetary scales to make it do anything noticeable. Unfortunately if we give our gravity-users planetary-scale powers over gravity it becomes trivial for them to destroy the planet. So instead we’ll limit their powers to changing the effects of planetary-scale gravity fields on much smaller massive objects. In other words, they need a powerful gravitational field to already be present, and they can make objects lighter or heavier within that field. I’m interpreting this as the ability to affect weight, not mass.
This ability has absurd potential for practical applications, most notably in construction and aerospace. The biggest challenge in designing a craft to reach space is that the fuel that generates thrust is usually the heaviest component of the craft. If you can turn a thousand-ton rocket into a five-pound rocket that still has millions of pounds of thrust behind it, the solar system is your oyster. Forklifts and cranes are a thing of the past on government construction projects: have a Gravity-user make the cargo featherweight, and give it a firm shove, and give the workers on the 20th floor heads up. And when it’s time for the building to come down, just quintuple its weight and get out of the way.
Of course, the ability to level buildings with a hand wave also has potential for military use (and more likely, terrorism). A gravity-user could pin soldiers to the ground with 10G, turn them to mush with 200G, pull planes out of the sky and sink tanks deep into the ground. With even a few gravity-users in play, the shape of warfare would change dramatically. No one can risk large forward-assaults anymore, lest they wind up sinking through the Earths’ mantle. Black ops is the name of the game and cyber-warfare reigns supreme.
That said, the logistical usefulness of Gravity-users far exceeds their use in warfare in my opinion. While they’re tremendously effective, they’re also a precious resource that dies to a snipers’ bullet just like an ordinary human. If you want your nation to be the most powerful, I think employing gravity users in your supply lines and manufacturing bases would be a much better allocation of resources then sending them directly into combat. They just make so many industrial processes so much easier; the demand for civilian services is so high I doubt many Gravity-users would turn to the military except in times of a draft. Then again, it might only take one to flatten the enemy capital into the ground.
I see Gravity-users as practically-minded upper-middle-class people mostly employed in construction. Their abilities are incredibly useful for everyday life, but aren’t particularly well-suited for direct combat, unless their reflexes are fast enough to drop bullets out of the air, but they would serve as a major deterrent to anyone planning an invasion. Because of high demand for their abilities from many sectors of the economy, I imagine they’d be very well-paid and live comfortable lives of productivity and comfort. The increased productivity they would bestow upon society would them icons of the workforce and heroes of labor, but since their success depends entirely on them getting their own hands dirty, I don’t see how they could ever own a business or ever truly leave the middle class.
Unlike gravity, electromagnetism is strong enough at small scales to be used without fear of destroying the planet. However, considering that electromagnetism is what hold atoms and molecules together, it could easily be used to vaporize... well, anything, including the entire planet, so let's set a limit and say that an EM user can only control electromagnetic fields at macroscopic scales.
Well, they can act like a magnet, or a lightning bolt. Create a positive charge on bad guy and a negative one in the atmosphere, and BANG!!! crispy bad guy. They could also create radiation, from radio waves to visible light to gamma rays, so you can microwave top ramen, become a human disco ball, give people skin cancer, or just annihilate them with gamma rays. Lasers might be tricky to pull off, but probably possible with sufficient training. You can wipe hard drives with a handwave, and you're every cyborg's worst nightmare. If powers include detecting EM fields, you could see in infrared, ultraviolet (probably not a good idea when visiting public restrooms), and detect all electronic equipment and brain activity around you. If they can manipulate existing radiation, they could curve light around themselves and go invisible.
Be careful with magnetism, since much like gravity it's very difficult to contain or aim. It would probably be possible though.
EM users are the Supermen of this world: they're flashy, versatile, immensely powerful in traditional superhero fights, and well-suited for public adoration. When your abilities revolve around lightning and lasers, stealth and discreteness isn't much of an option; even if you can turn yourself invisible for the approach, you’re going to light up the sky with fireworks when you actually strike. Also they don't however have any strong defensive abilities though (soon to be a common theme), so they would probably rely on governments to keep them safe and would serve publicly as either patriotic super-soldiers or semi-legal vigilantes. They would be the flaming sword of modern justice, the poster children of the force-users, and the only ones the public would regularly interact with.
Unfortunately there is no getting around the issue of subatomic manipulation for the next two. Unlike gravity and EM, the weak force has incredibly short range, since the particles that mediate it are massive and can only exert their effect over any distance at all thanks to the Heisenberg uncertainty principle. Herein lies a problem: by "short" I don't mean a few feet or a few inches or even a few nanometers, but 1/1000 of the diameter of a single proton. In other words, the weak force can't even be projected from one atom to another, or even from one side of an atom's nucleus to the other side.
So, you have two options. Either Weak users can project their abilities over distances or they can't, and can only affect what they can touch. The first option is very problematic since this ability is so stupidly strong, as we'll see shortly.
The second option makes this ability stupidly weak (no pun intended) since the distance between the electrons in your hand and the electrons in whatever you're touching is many orders of magnitude greater the weak force's range, meaning that your powers would only apply over your own body. This is problematic because this ability is stupidly destructive, as we'll see shortly.
So, problems of range aside, what can the weak force do? Well, it can change quarks (the particles that make up protons and neutrons in atomic nuclei) into other "flavors" of quarks. What does that do? It can change protons into neutrons and vice versa, which can change atoms into other kinds of atoms. Ha ha, you think! I'm an alchemist that can turn lead into gold and bullets into snowflakes! Well, no, because if you change the ratio of protons to neutrons in an atom, most of the time the result is an atom that is unstable, i.e., radioactive. Basically, your power is to turn any substance (or person) into nuclear fallout. If the ability were to taken to its logical extreme (which might be planet destroying territory), they could effectively turn any object into a neutron bomb.
So, going back to our options above, our weak user can either make anything, anywhere, radioactive, or they give themselves fatal radiation poisoning. Far more interesting, in my opinion, is to give their powers range over whatever they can focus clearly on, i.e an arbitrary short range of three meters. Given that EM users couldn't control their force at the atomic level, Weak users would require enormous concentration to do so, and would have to be close enough to their target to have some idea of its molecular structure (i.e. calcium carbonate for cement, water for people, etc). Due to the difficulty involved in feeling out and manipulating quintillions upon qunitillions of quarks, their powers would extremely difficult to master, and would probably not emerge until later in life, and perhaps only if they studied enough physics to understand what was happening.
Their powers can only be used to destroy, but unlike the Gravity users, they can control and direct them without world-shattering consequences. Their only defense is a crushing offense, but unlike the EM users, their offensive tools are not well-suited to public activity, and aren't accompanied by huge flashes of light and heat. For the average weak user, I'm imagining a cynical and secretive pariah with a very hard life unfolding before them. Maybe they were expelled from college after a particularly bad breakup, when their ex was taken the hospital one day with her flesh melting off her bones, and all her doctors died of cancer within the year. Maybe they wander the streets in rags holding a brown paper bag, muttering constantly about they could kill them all if they wanted to, yes they could, they'd kill them all! Or maybe they're sitting on a plush couch in an imposing skyscraper somewhere, ignoring their host's offers of wine and women, negotiating the price for the deaths of a nation's entire government. Whatever their path, they stay out of the spotlight, hide their powers as much as they can, and use them however they see fit.
It is really a stretch to make this is not a planet-destroying ability. The strong force is strong, 137 times stronger than EM to be exact. It's also known as the color force, because much like the weak force it acts on quarks, and in addition to "flavor" quarks have a property called "color" that is expressed through the strong force. To oversimplify, in quantum mechanics color always has to add up to white, so a red quark, a green quark, and a blue quark join together to form a white proton or neutron. Also a red quark could temporarily join with an anti-red anti-quark to form a meson. This color interaction binds quarks together extremely strongly. In fact, the energies involved are so large that nowhere in the universe today will you find a free colored quark that's not part of white structure. In fact, this energy, called quantum chromodynamics binding energy, is much larger than the actual mass of the quarks themselves (remember E=MC2). In short, most all mass in the universe is the "mass" of the energy bound up by the strong force as it keeps quarks glued together.
It's range is about 1000 times that of the weak force--still far too small to reach from one atom to the next--so let's assume its range mechanic works the same as the weak force. Now, what can it do?
By gaining power over the strong force, you have the ability to unleash obscene amounts of energy. The weakest possible implementation of this power that I can imagine is the ability to split and fuse atomic nuclei. If the atom you're targeting is lighter than iron, fusion releases energy and fission absorbs it. Heavier than iron and it's the opposite. How much energy? Well, think atom bombs, nuclear power plants, and well, the sun. E=MC2. again, emphasis on the C2. Let's do some quick math. Every second the sun converts 600 million tons of hydrogen into 595 million tons of helium, with the missing mass converted into energy. So fusing hydrogen converts (600-595)/600 = 0.833% of mass fused converted to energy. Take 0.1 Kg of hydrogen gas, and fuse it by manipulating the strong force. 0.1 Kg (M) * 0.833% * (9.0e16 (C2)) = 7.5e13 J = 90,000,000,000,000 J = 90 Terajoules = around one and a half Hiroshima bombs.
And that's a conservative estimate of what you could do with this power. In the modern universe, the strong force holds atomic nuclei together, it doesn't "get out in the open" much, so to speak. When it does, the universe turns into Quark-Gluon plasma. Bad times. I don’t have any numbers to back me up but I’m guessing that even the tiniest spark of QGP would, immediately upon creation, explode with the force of hundreds of nuclear weapons. An EM-user might be able to absorb the radiation from the blast, but not the heat or the shockwave.
So a Strong-user, using just the tiniest corner of their power, can unleash energies far exceeding those of the other force users. With a flick of a wrist they can wipe cities, countries, continents off the map. Even if we emplace arbitrary limits on their power to tone it back, they could kill and destroy anything and anyone they chose by creating microscopic nuclear explosions out of any matter at all. Their biggest challenge is not blowing themselves up in the process; to solve this issue, I suggest scaling up the range of the Strong-users’ abilities from 3 meters to 3 kilometers, an increase proportional to the difference in range between the strong force and the weak force.
Gravity-users are the industrious workers, EM-users are bold knights, Weak-users are roguish assassins—and Strong users are Kings. Gods, maybe, and despots, most likely. When you hold an entire nation’s nuclear arsenal in your fingertips, it’s not long before you start wondering why you’re bothering with working for anyone else. Also once the government discovers what you’re packing and decide it’s too dangerous to let you live, you don’t get much of a choice. They’re safe nowhere, and that makes them even more dangerous. Their only options are to disappear completely, or to make the world fear their wrath to the point where threatening their life doesn’t seem worth it. Perhaps they’d even start or inspire cultish followings that would populate their kingdoms and worship them as gods.
I imagine a world with Strong-users is locked in a cold war the likes of which the world has never seen. Every government with a brainwashed/loyal Strong-user, and every Strong-user who’s carved out a kingdom for themselves through violence and threats of violence, would constitute a nuclear power with an unlimited armament. Mutually assured destruction doesn't even begin to describe it. If Strong-users can be detected at birth, expect very few of them to reach adulthood.