Mass Drivers

Electromagnetically propelled munitinions, or mass drivers, are the most common style of weapon in human space. There's two main subcategories, railguns and coilguns. This tech is used for a lot more too, like launch loops. They both have the method of propulsion in common; electromagnetism. How they achieve this varies.
Railguns are generally bigger, and the smallest variants are portable anti-tank weapons hoisted on mobile platforms roughly the size of a bear. They range from tank cannons, spaceship turrets, or planetary defense installations.
A railgun uses, per the name, rails to accelerate a projectile. Specifically, the projectile is shaped so that it connects and allows a current between the two rails, which generates Lorentz force and accelerates the projectile. You do need a lot of energy to propell it to high speeds, but that isn't an issue with man-portable fusion power available. The projectile then breaks apart in such a way that only a rod is left, which deals the damage via kinetic energy.
Coilguns also propell a rod of metal, but they do it differently. Instead of two rails, there's a set of, well, coils. These coils are activated when the projectile passes through them, which gives it speed. Instead of a piece that conducts current and then breaks apart, a coilgun round just travels through a tube, surrounded by the coils. Coilguns are generally smaller, though they can be scaled up just as well as railguns. The smallest application is a coilrifle, which is standard in most militaries as an assault rifle. Due to their design, theyre also good as spinal weapons on starships, making for some really big guns.

Utility

Weapons. Personal arms, anti-tank guns, starship weaponry. Also launch assist and easier transport out of atmosphere.

Manufacturing

Raw resources, a printer or nanomachine plant, and that's all you need.

Access & Availability

Extremely accessible. Any rifle larger than a submachinegun can be made as a coilgun, and the tech is cheap. Mass driver weapons are the most common and available weapon systems in human space.

Complexity

Not too complex, especially for modern (late 2800s) manufacturing methods. Easy to maintain.

Discovery

The tech has been under development and experimentation since the mid-20th century, but it was in the 21st century that Fusion power and its miniturization had gotten to a point where the power draw of mass drivers became manageable. Prior to that, it had been in use mainly on spaceships or as launch assist from the 2040s.