MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.

Uppy - The next open source file uploader for web browsers

Beeceptor - Unblock yourself from API dependencies, and build & integrate with APIs fast. Beeceptor helps you build a mock Rest API in a few seconds.

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.

Webhook.site - Instantly generate a free, unique URL and email address to test, inspect, and automate (with a visual workflow editor and scripts) incoming HTTP requests and emails.

Uppy.io - Next open source file uploader for web browsers