Gas Giant Lab
The Gas Giant Lab does research on the gas giant settlement ship which deploys into a gas giant settlement platform. The gas giant settlement platform allows settlement of a gas giant. The higher the level of the gas giant lab the higher the level of the platform deployed from the gas giant settlement ship.
The Observatory allows the construction of probes and colony ships at the shipyard. It also provides a list of all your active probes and the stars they are observing. A higher building level allows more probes to be constructed. You may only have one Observatory on a planet.
Planetary Command Center
The planetary command center (PCC) houses the central government for your empire. This is your "flag in the ground" that lets everyone know you've staked your claim to a planet. It provides some basic resources and and storage for those resources both of which increase with the level of this building. The planetary command center also provides some critical reports on your planetary activities such as total resource production and total resource storage for the planet it's constructed on. It's one of the most versatile buildings in the game, but it's also very expensive to upgrade.
The Terraforming Lab is where research is done on the production of terraforming platform ships. Terraforming platform ships deploy into terraforming platforms which allows you to colonize planets your species wouldn't normally be capable of colonizing. The level of the building determines the level of the platform that is deployed from the ship.