a real-world grep. this might be solved in my lifetime, since books, notes, etc are all moving to digital. sometimes i just wish i could grep for x and it would find x in all my books, notebooks, etc.
I'm actually working on this problem. It's remarkable the amount of content we actually generate and the number of services/mediums we generate them on. Simply fetching all the data and hosting it centrally is a large enough problem, let alone indexing all of it.