In Event Horizon, starbases appear when player is conquering any faction's capital. They're very strong, but those close to the center of the galaxy are unarmed, regardless of faction. When the player goes further, each faction has it's own starbase build.
Veniri bases are equiped with pulse cannons and 4 M11 drones. However, they do not possess drone factories, so their drones will not respawn.
Bushrak bases are equiped with three M21 drones and Heavy Missile Lanchers, so agile ships and ECM Jammers are recommended.
The Korerans' starbases are equipped with Heavy EMP Torpedoes and four M31 drones, however they do not have any drone factories so the drones will not respawn. An ECM Jammer and an agile ship are recommended in order to evade the torpedoes and drones. A high-firepower gunship will probably fail due to EMP stunlock.
Taraniak bases have four M41 drones and Heavy Lightning Cannon, so as long as you aren't directly next to them, you will be safe.
Sayjix bases only have four M51 drones.
Jurgans' bases are armed with dual Heavy Acid Missiles in every weapon mount and two Embryo Mk2 drones. A ship agile enough to avoid missiles and acid clouds is recommended.
Zumbalari bases are equipped with heavy neutron blasters and Missile launcher M3s.
Neganari bases are equipped with just Mass Drivers (M2?).
Daazen starbases have Heavy Antimmatter Bombs (M2?) on each weapon mount, which essentially create an area of denial around the superstructure. They are heavily shielded, so ships like the ISS Galleon, which can be with outfitted 2 Heavy EMP Torpedoes, are easily able to destroy them from a safe distance, as, in the Galleon's case, EMPs do critical amounts of damage to shields. Long range weapons of any sort, however, are viable.
Unknown Starbases have Tachyon Beams on each weapon mount, they deal extreme damage at the same range as the Railgun if they fire a full charge. Luckily due to its charging time, a ship with high DPS such as a Stalker can destroy it before it gets a full charge.
The Empire's Starbases are equipped with triple Rocket Launcher M2s on each weapon mount. Also they have 6 imperial drones, so at first player should focus on destroying them, because they can quickly repair base and deal much damage to player's ship.
In current version The Swarm has no Starbase, and there's no information on them possibly being added in the future.
Pirate bases, like the Daazen's, are well shielded. They're equiped with Holy Cannons and 3 Santa Drones with drone factory, so it's recommended to use long-range weapons.
In EH: Frontier, the player owns and defends his own starbase. He can also manage the base's equipment, just as he can manage that of his ship's. The starbase is majorly composed of blue slots, allowing the prodigious use of armor, shielding, drones, or a concoction of all three.
The base can be equipped with any weapon that is at least 2x2 slots big.