Most space combat is dominated by kinetic energy weapons, rocket-propelled guided missiles, and lasers.
Kinetic energy weapons take many forms, from pellets to bullets and darts. These depend on high velocity to do their damage. They are propelled by various means, ranging from chemical propellant in old fashioned cannons to hybrid ETGs (electro-thermal guns) and the more experimental electro-magnetic coil guns. ETGs are currently the most widespread technology. One problem with kinetic energy weapons is that their projectiles become space junk that remains dangerous long after the battle is passed. Projectiles have been developed that automatically disintegrate some time after firing, but these are more expensive and have not been universally adopted yet. ETG weapons are generally available in 10mm, 20mm, 30mm, and 45mm bore sizes.
General Products has been the gold-standard manufacturer of starship ETG weaponry for several decades. InterCore, Omicron Industries, and Starck Technologies (a recent addition from Annyrion) all produce kinetic energy weapons, as well.
Rocket propelled guided missiles (or “torpedoes” as some traditionalists still insist on calling them) are expensive but generally have a greater chance of hitting their target, since they can respond to the evasive maneuvers of a target ship. They can also carry a large explosive charge or other warhead. Short-range fighter-based weapons such as Omicron Industries 'Lancet' unguided rocket pods and 'Shkval' unguided rocket-propelled bomb are also included in this category.
Sternmetal Horizons manufactures the HAWK, EAGLE, and PHOENIX anti-ship missiles and launch systems, and has licensed the technology to Namiki Industries. In addition, InterCore and Omicron Industries both have weapons divisions producing various missile designs.
Lasers have recently been reintroduced as shipboard weapons. Their advantage is that their beam literally moves at the speed of light and therefore is very accurate, when compared to ETG kinetic energy weapons. The tradeoff involves the large banks of energy storage units required to supply power to the laser. If these energy storage banks become damaged, the laser loses effectiveness or may not have sufficient power to function. Lasers are generally rated according to power requirement: R5, R10, R15, and R30.
Some research has been made in the area of particle accelerator weapons, but the only existing prototypes are in the form of a spinal-mount linear accelerator, with accelerator length corresponding directly to weapon effectiveness. Circular-track accelerators currently have too great a mass penalty in the form of shielding to permit safe use onboard starships. Barring breakthroughs in radiation shielding technology, particle weapons may be limited to ships with long hulls.
Seibu-Kaihatsu Heavy Industries, InterCore, and Omicron Industries manufacture directed-energy weapons. Starck Technologies has recently entered the market, as well.
Spaceship defenses consist of passive defenses - armor - and active defenses - evasive maneuvering and electronic countermeasures (ECM). No progress has yet been made toward developing any kind of force field to protect ships.
ECM defends ships by attempting to spoof missiles into missing. While stealthy radar-absorbing/deflecting coatings are available, it is nearly impossible to passively conceal a ship's location in space due to differences in temperature when compared to the cosmic background. This is where ECM comes into play by confusing or even sometimes disabling sensors on incoming missiles. Nearly every corporation that builds starship components also has a division that manufactures shipboard countermeasures systems.
Evasive maneuvers, contrary to mental images conjured by people who have grown up on movies like the Star Wars series, are primarily an effort to avoid contact with incoming rounds, laser energy, and missiles by putting as much space as possible between your ship and the opposing ship's weapons without actually breaking contact. Moving your ship so that something else lies between you and incoming rounds is also considered evasive maneuvering. While some random movement at a distance can make it more challenging to hit you, all starships - even “space fighters” - are bound by the same laws of physics, and the closer you get to an enemy ship, the less likely you will be able to simply dodge incoming fire.
Armor is the final protection a ship has against weapons that make contact with the ship's hull.
In the past, exotic weapons have been experimented with, including “spurt bomb” gamma-ray/x-ray lasers, but due to the general prohibition of nuclear weapons (a nuclear explosion is used to power the laser), they have not made a comeback.
Standard missiles could theoretically carry a nuclear warhead, but this has not been done since the Apocalypse War. Since Earth was devastated in large part by nuclear weapons, recoms have developed a very strong distaste toward building or using them. Also, it is very hard to secretly produce nuclear fuel for bombs since fission reactors have entirely been replaced by IEC fusion, which does not produce fissile materials.