A faction of vast consciousnesses that transferred themselves into machine bodies, so-called "Frames", near-indestructible masterpieces of engineering with custom-fit abilities and the capacity to hold a vast mind. They have been hibernating for the past 68,300,000 years in their capital system, not unconscious, but thinking and "talking" with each other. They are
They are (or were) called "The Old" and sometimes synths, but their own name for themselves is "The Eternal Thinkers" (in English translation).
The Frames of these ancients are many and varied, but their systems are nearly identical (with exceptions) and they all use the same material (or variants of it). It is called "Flowing Metal" in their language, and after being "programmed" into a specific set of movements it never leaves them except under extreme conditions (the hearts of supernovae, neutron stars, etc.). It is possible that they developed a technology that allowed them to control material on a molecular basis, but much is unknown about its manufacturing and properties, even among themselves, since the masters of their manufacture were broken mentally and are highly unstable.
Each Frame is custom-tailored to its wearer and has unique armaments and abilities. You can find about any type of armament imaginable among The Old. Plasma-throwers, EMPs, rocket launchers, laser drills, plasma swords, they have it all. All Frames are capable of flight in space and in most atmospheres (with two exceptions) and have an almost inexhaustible core of super-concentrated energy.
Today, there aren't any empty Frames except for a few hundred basic ones in three caches, one of them in the Valkyr System and the other two at relatively remote bases. Those, however, lack standard powercores and are the emergency transfer bodies. They are mostly the defects from manufacture.
Originally, The Old were a race of humanoids with about 150-200 year lifespans. They started augmenting their bodies a few thousand years A.U. (after unification) and started building bodies a few thousand years later. Their lifespans lengthened and a hundred thousand years A.U. lifespans tens of thousands of years long were commonplace and their minds started to become more and more complicated. They grew and colonized a large part of the Sagittarius dwarf galax, having discovered superluminal drives a long time ago. At 500,000 A.U. they had developed "Flowing Metal" and development of Frames as they are today started. At around 1M A.U. Frames as they are today were perfected and The Old became essentially immortal.
However, there was a small portion of The Old that wanted dominion over the others and soon after the perfection of the Frames they started building Frames capable of destroying other ones with some sort of disintegration system (it is unknown how it worked). In 160,081,241, they started a war with themselves, assassinating most of the Master Craftsmen right at the start and killing hundreds of thousands with their couple thousand of killers and declared their ultimatum. The very last three Master Craftsmen that survived the initial onslaught managed to get hold of one of the enemy Frames (with the help of one who betrayed the betrayers) and reverse-engineered their technology into small grenade-like devices. The majority eventually managed to destroy the conquerors and wiped them out to a man, with the exception of the one who repented near the start. The war lasted nearly a thousand years, however, and the last Master Craftsmen perished along with most of the civilization. Nearly 90% of the population died (ironically after becoming essentially gods) and most of the structures they built. The last few after the so-called War of Gods stopped nearly all of their activity, only sending out drones to study the world around them more. They have become sages in most everything and they probably know more about the universe than else.
They had sent drones out into the Milky Way and met the Terran Alliance, though they never find out who or what The Old were. They also observed the Rin and helped multiple civilizations in remote places of the Way with technology, which is one of the few places that actually know of the synths.