Nuclear overhaul mod. Fly to Aquilo as your first space platform destination. Or second, or third.
Mods introducing new content into the game.
Transportation of the player, be it vehicles or teleporters.
Trains are great, but what if they could do even more?
New ways to deal with enemies, be it attack or defense.
Things related to oil and other fluids.
Furnaces, assembling machines, production chains.
Changes to power production and distribution.