Ask HN: What tool do you use to manage your app's assets/images?

An app, whether a SaaS or mobile app, needs many images of different sizes for all different platforms: - the iOS App and Google Play stores (icons in sizes X/X'/X''/..., screenshots, ...) - your app's Facebook page (icon in size Y, cover, ...) - its Twitter account (icon in size Z, cover) - ad campaigns - ...

What tool(s) do you use to manage (upload/resize/edit/version) them?