Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
Uppy - The next open source file uploader for web browsers
httpbin(1) - HTTP request and response service
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.
Endpoints - View and respond to requests on an HTTP endpoint
Uppy.io - Next open source file uploader for web browsers