File.io
Super simple file sharing, convenient, anonymous and secure

Filestack File Uploader & File Upload API.
Filestack API is a free Cloud Storage & File Sharing API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Add a sleek file uploader to your website with two lines of code. Upload from local disk, Dropbox, Instagram, Google Drive, and 20+ integrations.
Details from filestack.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Super simple file sharing, convenient, anonymous and secure
The Filestack API is provided by Filestack (filestack.com). Add a sleek file uploader to your website with two lines of code. Upload from local disk, Dropbox, Instagram, Google Drive, and 20+ integrations.
Yes. The Filestack API is listed in the Cloud Storage & File Sharing category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Filestack API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Filestack API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Filestack API is served over HTTPS, so it's safe to use in production.