Railguns

The classic railgun consists of a pair of rails through which electricity is sent to produce an accelerating magnetic field. Ammunition, typically highly dense depleted uranium is fired from the railgun at a velocity exceeding 11,000 ft/sec. At such a speed the kinetic energy yield is superior to an equivalent amount of explosives in the same round. In space the range of this kind of railgun is limited and it is primarily of use only against stations and other predictable or stationary targets.
A gravity pulse railgun uses a gravity gradient to provide acceleration. Unlike the classic electromagnetic railgun the rounds do not need to be ferrous (or have a ferrous sabot.) That means conventional smart ammunition can be used. This allows for a great variety of ammunition types to be employed. Smart ammunition is most effective at short ranges, usually no greater than planetary orbit, where they are effectively employed as precision guided dead fall ordinance. At any range over a few hundred miles solid core ballistic hyperdense rounds are used.
In space combat railguns can fire rounds from 40mm to 100 mm. Most are setup to feed from a variety of magazines to allow selected fire from the fire control or gunner's station. They are capable of both a high rate of fire or single shot operation.
In the anti-missile roll gravity pulse railguns typically use canister shot,  a round consisting of any where from a dozen to a hundred beads of hyperdense designed to create a cloud of destructive material to kill incoming missiles.
Railguns are most often used in an anti-missile role, and against encroaching small craft. Used with rounds outfitted with gravity pulse warheads a railgun can even damage force screen protected targets. They are very effective against planetary targets and conventionally armored military craft.
Ranges are still short compared to missiles or energy weapons, but the flexibility of payload combined with high rate of fire makes the railgun an important niche weapon in space combat.