The weapons listed don't represent even a portion of the various guns found in the far future. They should however give the players an idea of the danger level found in the hands of combatants.
While the concept is millenia old, Firearms still play an important role in combat. They have several advantages over lasers and power guns: cheap, low firing signature, and versatile ammunition types. The "ET" ammunition type represents "energy transfer": a variety of projectiles that go "splat" into the target (equivalent to jacketed hollow point rounds in the 21st Century). The "gauss rifle" (aka "rail gun" or "coil gun") was commonly used for nearly a thousand years, and remains common on some outlying colony worlds. Newer colonies employ the more versatile "colonial musketoon" for similar purposes.
Grenade Launchers persist also, with the concept of low-velocity, indirect fired projectiles dealing a variety of damage. Flamethrowers have seen some use against aggressive flora and fauna on colony worlds.
Lasers remain the weapon of choice for Spacers, and from about the 22nd Century to the 37th Century were the only personal "energy weapon" available. In Zero-G conditions, they are often the best choice for personal defense. Most weapons lasers (but not all) work in the high-violet or low UV spectrum; thus users and friendly forces must wear protective goggles to prevent reflection burns on the retina. Many forms of laser beam disperson -- usually incorporated into smoke clouds -- are known and used.
Power Guns go by many names, at different times, in a variety of languages: PBW, blaster, plasma gun, beamer, fusil de puissance, plasmatron, plasmagewehr, energion, etc. Before the widespread use of force field technology, these weapons were never small enough to put in the hands of an infantryman; so, the examples given represent advances made in the last century or so. Particle beams have a advantage over lasers in that the particles have more impact damage on the target than the massless photons of a laser beam. There is better penetration as well, with the penetration climbing rapidly as the energy per particle increases. Particle beams deposit their energy up to several centimeters into the target, compared to the surface deposit done by lasers. Lasers are inherently longer-ranged than neutralized-charge particle beam weapons, however (charged particle weapons have their own problem; and neutron beam weapons don't 'self power' the nice way that charged ones do). Power guns also produce a brilliant flash and beam; the beam will set fires along its path, and produces a thunderous roar. Operators must wear thermal protective gear. Power guns are also poor at pentrating force field defenses.
The 90mm Missile Launcher is reasonably capable for colonial and low-intensity warfare, but must not be thought of as being even minimally useful in major conflicts. The complicated interplay of sensors, defenses, deception, agility and encryption found on a Real Big Battlefield remains beyond the likely capabilities of player-characters.