The Dropbox C++ library provides developers access to the Dropbox core API, wrapping the REST API in C++ classes and objects for Qt. Dropbox is a file storage, sharing, and synching service that allows users to store, share, and sync their files.
The Google Realtime API has been deprecated, and the API will be shut down in January 2019. The company provides other products such as Google Cloud SQL, Firebase Realtime Database, and Google Cloud Firestore which should meet developers application development requirements.
SmartFile, a leading FTP and file sharing solutions provider, has released "SmartFile for Developers", described by SmartFile as "the World’s First Developer Centric PaaS for Files." SmartFile for Developers is a file management platform-as-a-service (PaaS) that allows developers to integrate web, smartphone and internal applications using the SmartFile API.