Mockoon

Mockoon is a free, open-source application that simplifies the process of creating and running mock REST APIs. It's designed to be the easiest and quickest solution for developers, running locally on your machine without needing an account or remote deployments. This makes it an ideal choice for high-security or privacy-conscious environments.

Mockoon provides a complete toolset to handle any situation:

• Advanced Customization: Create highly realistic scenarios using dynamic templating, a flexible rules-matching system, and JSON databases. You can also simulate real-world conditions and test edge cases.
• Seamless Integration: It integrates perfectly with your existing workflow. Use it with the OpenAPI specification, forward requests to your actual APIs, or use the proxy mode to record and replay HTTP traffic.
• Run Anywhere: Take your mock environments wherever you need them. Use the CLI and Docker image to run mock servers in CI/CD pipelines or deploy them to serverless platforms like AWS Lambda.
• Team Collaboration: For teams, Mockoon Cloud offers real-time collaboration, allowing you to share and manage your mock APIs effortlessly.