Luna

The sole natural satelite of Earth, renamed from a simple Moon when Mankind colonized it - and did the same with numerous other moons within the Solar System. Today it remains within the - pun probably intended - political orbit of Earth, despite having rather problematic history with it over the Secession War.
It has suffered a lot during the Blackout, leading to its current status as de facto equal to one of the major terran governments (in the past, it was notably more important than any of those, though it was still far inferior to the Earth as the whole). Luna is in the right position to develop ambitions, although where those will bring her is anyone's guess.

Geography

Moon isn't an oceanic world, but it has a rather expansive hydrosphere composed of two large and mostly connected oceans and numerous endorheic water basins with no connection to the ocean, typically depending on the rainfall to sustain themselves (although this has been changed by human engineering - expect many manmade canals made to control the water level of such places).
The low gravity means high waves, up to ten meters tall (although also rather slow if giant). This makes the coastline a not very pleasant place to live. There is a single landmass, and a number of smaller islands, typically wrecked by tidal waves on an almost daily basis. It's also a rather rainy place, as the air currents make a light rain fall almost every night, almost everywhere. This is at least partially caused by large temperature amplitude between the day and night.

Ecosystem

Varied, although a large part of it has been created as natural preserves. Luna has numerous landlocked lakes and islands with relatively stable climate (if you exclude the waves) - as a result, many of those were chosen to host an endangered local ecosystem from Earth, which was deemed to be compatible with local climate (and somewhat adapted to the low gravity). While terran biosphere is no longer threatened by extinction, expect many regionalized and self-isolated ecosystems on Luna.

History

Luna was the place of the first permanent human habitat outside of Earth. It was also the field of the first extraterrestrial ground warfare of Earth, as it become a battleground during the Third World War. Just like the Venus, it was initially colonized by the Union of Progress and Freedom. The Alliance for the Preservation of Democracy attempted to counteract during the War, but ended up being entirely driven off Luna.
This didn't last, as the UPF lost the war on Earth and subsequently collapsed. Luna become the place of the last stand of the UPF forces, finally dislodged in 2090 during the short Lunar War. Luna remained in the Alliance sphere of influence until the Fourth World War, during which the remaining Union loyalists staged a brief civil war, that they lost. After the war ended, Luna turned independent, although not before driving the rebels off-world.
It has continued existing as the United Lunar Republic ever since, becoming a notable power. Unlike Earth, however, its low gravity made it a bit more receptive to the wonders of transhumanism (the technology could make lives easier), resulting in large degree of casualties during the Transhuman Wars. And then came the Blackout.
Today it is in a rather complicated situation. It is a relatively prosperous, capitalist economy housing numerous megacorps (with an unknown but possibly large degree of influence over their host) and having an expansive economy. It's also one of the centers of the shipyard assembly. It can also feed itself, and that means a lot nowadays. However, it also has a rather thorny relations with Earth, as Luna sided with the Commonwealth during the Secession War, something many of the terrans refuse to forget.
It also appears to be developing certain ambitions, although it is unknown how far those will take it.

Luna
Summary
Distance from Sun: 149.5 mil. km
Distance from Earth: 0.38 mil. km
Diameter: 3484 km
Solar Constant: 1.98
Mass: 0.0123 Earths
Mean density: 3.44 kg/l
Orbital period: 27.322 days
Day Length: 29.53 days
Rotation Axial Tilt: Similar to Earth

Avg. Temperature per Latitude
poles: -22 C
75 deg: -2 C
60 deg: 6 C
45 deg: 12 C
30 deg: 18 C
15 deg: 22 C
equator: 27 C

Astrography
Type: Moon [Terraformed]
Location: Earth Subsystem
Status: Colonized
Population: ~100 mln.

Governments
United Lunar Republic