Ask HN: Open-source API for publishing files updates?

I'm looking for a solution that would allow users to upload resources through a web interface and these resources would be available for client apps so they can be updated. For example:

- Client app consumes images

- Client app asks the API: "What's new since yesterday?"

- API returns a list of files to download

- Client app downloads the files and updates the time it checked for updates

I assume this is a fairly common situation and I would like to avoid having to build something like this if it already exists.