A Matrioshka Brain or Jupiter Brain is a hypothetical megastructure in which the energy output is used as a giant computer. This can appear in a Dyson sphere.
A Matrioshka Brain could also be classified as a cosmic entity given the the high possibility of it attaining some level of sentience.
Computations inside a Matrioshka Brain could be sped up using traversable Lorentzian Wormholes.
They could also be used as a means to upload the consciousness of an entire species into a virtual environment, making them a kind of digital heaven.