It turns out that, technically, I was correct. I could use MongoDB as a key-value store for caching, much like I could use my Mazda 3 as an amphibious assault vehicle. In practice, neither would be optimized for those use cases.
Use the same principle if you have to build MongoDB work queues.
Original title and link: Redis and MongoDB Can Work Together to Perform Distinct, Complex Queries ( ©myNoSQL)