Insane, intensely private, planet-engulfing nanite swarm.
Their entire planet is covered in beige nanobots. It is unknown whether they were a terrible accident, a deliberate weapon, or a resource mining project, but what is known is that they have been thorough. Nothing is left except for the radioactive core of the planet. The nanobots are very good at assembly, and will do so if they are given the raw materials. However, they are very secretive about their design - they will self destruct if removed from the rest of the Beige Goo.