These are the four
that humans are studying so far. Here's a hint about a fifth
Now let's step outside what people have the math to explain, and just look at patterns.
Everything is connected. Some people don't think there is a "universal force" because they can't explain it yet. Others are avidly looking for it. The forces we notice are like the fingers on a hand -- connected at the base, yet capable of doing separate things. The fact we haven't found the hand yet doesn't mean it isn't there. We can infer its presence based on surrounding patterns and how the known forces behave in relationship to each other. Just as we used to think of electricity and magnetism as separate, and now know they're different aspects of the same thing, so it is with the rest of this stuff.
It's very clever of people to go looking for more chapters of information by examining patterns of known chapters, such as observing that "the elusive “protophobic X boson" — a particle that only interacts with electrons and neutrons, instead of the electromagnetic combo of electrons and protons." Now just go down the list of possibilities, and you will find a bunch more chapters. What are the other combinations of particles that forces could involve? If you find particles that are new to you, those can lead you to forces you have not yet explored.
Humanity is just starting to get into the less-obvious stuff. Seriously folks, the easiest way to find that is to grid what you already have and then look at the gaps. Where are you not seeing influences between combinations of things? Those might well exist but they are less apparent so you will have to hunt for them. It's a lot easier to find things if you have some idea where they would logically be.
Same with applications. We base technology on electromagnetism and nuclear physics. So too, it is possible to base technology on gravity. I don't mind how slow this is going, because we don't have the social technology to handle that level of physical technology, and it's pretty easy to cause planetary-scale damage with lab accidents in that field. Let's just not hand the blowtorch to the toddlers. But it does work.