Uppy - The next open source file uploader for web browsers
Filestack - Filestack is file uploading software designed for cloud usage applications.
tus.io - File Uploads
CarrierWave - Solution for file uploads for Rails, Sinatra and other Ruby web frameworks.
Uploadcare - CDN, content delivery, content delivery network, file handling, image processing, cloud storage.
Transloadit - Versatile file uploading and processing service for developers