Gas Giant
Gas giants are large worlds that have extremely dense atmospheres and very strong gravity. The atmosphere is so dense that it is liquefied and forms a incredibly deep ocean world. It is possible to dive into the ocean of liquefied gasses with a submarine or a submersible spacecraft.
A gas giant can have one large moon in orbit, which is the moon equivalent to a normal planet.
Harvestable Resources
Gas giants are normally rich in various atmospheric resources which can be harvested using harvester bay equipped spacecraft. This is normally also very advantageous as the high atmosphere density means greater harvest yields. They will contain the same set of resources regardless of their orbit zone.
Atmospheric Resources
Harvester bay: Atmospheric Condenser Bay
Particle Resources
Harvester bay: Particle Collector Bay
Colonization
At the center of a gas giant is a rocky core. The rocky core can be colonized with buildings and and cities just like normal worlds.
Construction is a harsh environment, but it also requires grav couplings to counteract the strong gravity.
Core Resources
The rocky core has a few unique resources that are not found anywhere else.