The worlds of zinc and lead come together.
Collections of mods with tweaks to make them work together.
New places to build more factories.
Augmented or new ways of transporting materials - belts, inserters, pipes!
New ways to deal with enemies, be it attack or defense.
Map generation and terrain modification.
New Ores and resources as well as machines.
Things related to oil and other fluids.
Furnaces, assembling machines, production chains.
Changes to power production and distribution.