Core components

Core components are class design elements which are automatically designed upon being researched. Some core components such as asteroid mining and terraforming modules are automatically upgraded as the linked technology improves, preventing you from having to constantly refit and upgrade their parent ships to keep up with the tech level.

Basic Systems

Nearly every ship, and some PDC classes need one of everything here

Bridge: Provides command and control functionality to larger ships that are classed over 1000 tons.
Crew Quarters: Provides life support for additional crew, comes in a number of sizes.
Engineering Sections: Reduces failure rate of the ship it is attached to, also stores a small amount of maintenance supplies.
Fuel Storage: Stores fuel, oddly. Available in progressively smaller sizes and comes in armored varieties.
Maintenance Storage Bay: Drastically increases the amount of maintenance supplies the ship can carry. However, it actually increases the failure rate of the ship so must be paired with Engineering Spaces.

Passive Sensors

Geological Survey Sensors: Generates geosurvey points when tasked. Necessary for finding minerals, new techs improve efficiency in the form of new Improved, Advanced, etc. components.
Gravitational Survey Sensors: Generates gravsurvey points when tasked. You need these to find undiscovered jump points, new techs improve efficiency in the form of new Improved, Advanced, etc. components.

Transport and Industry

Cargo Handling System: Reduces loading time of colonists, cargo and troops. New tech improves efficiency in the form of Improved, Advanced, etc. components.
Cargo Hold: Cargo in this context refers to minerals, installations and pre-made components. It's generally a good idea to build these in multiples of 5, if you have to build them.
Asteroid Mining Module: These modules perform exactly the same function as a mine, but ONLY over asteroids and comets. They are automatically upgraded as mining tech progresses.
Terraforming Module: These contribute the base atmospheres per annum of your current technology level.
Sorium Harvester: Used to refine Sorium into fuel from Sorium gas giants. Base rate is 20,000 litres/year/harvester module, upgradable via research. Harvester modules consume 1 ton of Sorium per 2000 litres refined. This conversion rate does not change with additional research.

Other Systems

Flag Bridge: Allows stationing of a Task Force HQ (officers & staff) in a ship rather than from their ground offices.
Hangar Deck / Boat Bay: Allows parasite ships to be housed on the mothership.
Orbital Habitat Module: Allows up to 50,000 people to live in orbit of a planet/moon/etc providing workers for ground-based installations.
Recreational Module: Allows ships in the same location to go on shore leave.
Ship-to-Ship Tractor: Allows one ship to link to and move another ship, useful for moving disabled ships, orbital habitats and shipyards.

List of Components

Engines and Power Plants: Engine • Fuel Storage • Jump Engine • Power Plants
Beam Weaponry: Beam Fire Control • Lasers • Particle Beams • Mesons • High-Powered Microwave • Plasma Carronade • Railguns • Gauss Cannons
Missile Weaponry: Missile Fire Control • Missile Launchers • Magazines
Defensive Systems: Armor • Shields • CIWS • Sensor Jammer • Fire Control Jammer • Missile Jammer • Decoy Launcher • Cloaking Device
Maintenance and Repairs: Engineering Spaces • Maintenance Storage Bay • Damage Control • Maintenance module
Carriers and Fighters: Hangar deck • Fighter Pod Bay
Sensors: Active Sensor • EM Sensor • Thermal Sensor • Geological Survey Sensors • Gravitational Survey Sensors • ELINT Modules
Command and Control: Bridge • Flag Bridge • Auxiliary Control • Science Department • Main Engineering • Combat Information Centre • Primary Flight Control
Transportation: Cargo Hold • Troop Transport Bay • Cryogenic Transport • Passenger Accommodation
Logistics: Cargo Shuttle Bay • Refuelling System • Ordnance Transfer System • Tractor Beam
Production: Orbital Mining Module • Sorium Harvester • Terraforming Module • Jump Point Stabilisation Module • Salvage Module