Filestack - Simple file uploader and robust APIs for uploading, transforming, and delivering any file into your app. Filestack is a collection of tools and powerful APIs that make it simple to upload, transform, and deliver content.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Cloudimage - Cloudimage.io is the easiest way to resize, store, and deliver your images to your customers through a rocket fast CDN.
Filecamp - Digital Asset Management & Online Proofing tools beautifully integrated, into one secure and cost-effective solution. Manage all your digital marketing assets from your own good-looking, easy-to-use spot in the cloud. Unlimited users in all plans!
Uploadcare - File uploading, media processing & content delivery for modern web apps
Nubo - A self-hosted file sharing application in Haskell.