I'noxia was a distant planet, which was home to a collective civilization called the I'noxians. Everything from the people, to the buildings themselves are made from a substance called N-10, which is a sort of programmable matter made of nanomachines. The I'noxians were created to observe and recreate doomed worlds on their own world, for posterity. (Supergirl: "Out of the Past")
The outdated planet fell under the influence of Brainiac, who put the Cyborg Superman in control of it. Their plan was to lure Supergirl there, who was suffering from Kryptonite poisoning, and to capture and study her to better understand its effects. To that effect, the I'noxians helped recreate Kara's childhood home to put her at ease, before the Cyborg enacted his own plan to take her body for his own, in order to learn who he was before he became the Cyborg.
However, the plan backfired when the Cyborg regained his memories, and, realizing he was Zor-El, Kara's father, he gave Kara her body back and helped the I'noxian collective leave the planet, escaping Brainiac's attack. (Supergirl: "Out of the Past")