The tesseract Is a Hyper-dimensional entity capable of storing huge amounts of energy and matter and making them available everywhere (WIP looking for testers)
Mods introducing new content into the game.
Transportation of the player, be it vehicles or teleporters.
Augmented or new ways of transporting materials - belts, inserters, pipes!
Armors or armor equipment.
Entities which interact with the circuit network.
Changes to power production and distribution.
More than just chests.