The Alien Entities are the machine constructs of an unknown alien race that appeared during joint NATO-Livonian training exercises in the fictional country of Livonia.
In the non-canon DLC Arma 3: Contact, they visit the Earth over the course of one night, seemingly to dig up and remove incredibly energy-dense nodes from a vast underground network of unknown origin. Their arrival was preceded days earlier by an unusually intense neutrino storm, and their arrival itself caused a localized EMP-like event that created confusion among the NATO forces.
The aliens are represented on Earth by a variety of autonomous drones, which range from sky-scraper-sized constructs capable of faster-than-light travel to car-sized defensive and scientific machines. Their constructs demonstrate a mastery over gravity as well as incredible agility and speed, along with formidable energy-based weaponry and pulsing force-fields.