An SSPGD (Superradiant Scattering Power Generation Device) (also called a Penrose Sphere) is a large spherical mirror built around a spinning supermassive black hole. This device harvests energy from a rotating black hole via the Penrose Process. This process was first theorized to exist by Roger Penrose in the 20th century. The first recorded Penrose sphere was constructed around the black hole V616 Monocerotis.
In the entire universe, there are about three hundred thousand SSPGDs, with the average civilization having several, with the most having tens of thousands. A majority of the power of the universe is harvested this way.
The Ergosphere is a region of space-time around a rotating black hole. The Ergosphere rotates with the black hole, in an almost whirlpool-like fashion. The size of the Ergosphere is dependant on the size and angular momentum of the black hole.
Energy Harvesting Process
A beam of light shined into the Ergosphere at a proper angle would gain energy from the black hole (up to 20.7 percent). The purpose of a Penrose sphere is to trap this light and reflect it back towards the black hole multiple times, resulting in a huge profit of energy. This energy is not infinite by any means, every time a beam of light is shined in, a bit of the black hole's rotational energy is lost. After trillions of years, the black hole would eventually lose all rotational energy (with current methods and estimations).
This device is capable of being weaponized. The way to do this is to never extract energy from the sphere and let it build up. This energy build would eventually result in a catastrophic failure in the sphere, releasing energy equivalent to that of a large supernova. This is the most powerful weapon that could feasibly be made by a species. The black hole is not consumed in this process and can be used again and again. More here.