Question: has anyone seen one or knows of someone who is trying to build one?
Longer version: Proof or work wastes energy by design, and while proof of stake is less wasteful, it is still not remotely as efficient or performant as modern banking systems. Proof of (hard drive) Capacity is wasteful of device production and running energy, and proof of elapsed time seems to be a lottery system, which looks likely to be difficult to secure in practice.
Also proof of work can be translated into anything, like serving websites, images, processing video, and in that case is equivalent to any cloud or hosting provider