Adds Carbonate, oxide, sulfide, and fluoride minerals.
Mods introducing new content into the game.
Augmented or new ways of transporting materials - belts, inserters, pipes!
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.
What it says on the tin. In the inventory, it is under the Unsorted category, while everything else is under the Chemistry tab (I have the chemistry-tab mod installed).