Thunder Client - Rest API client for VS Code, lightweight Postman alternative
Beeceptor - Unblock yourself from API dependencies, and build & integrate with APIs fast. Beeceptor helps you build a mock Rest API in a few seconds.
Ping-API - Automated API testing and monitoring.
MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
HTTPie for Terminal - Developers all around the world rely on HTTPie for API testing.
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.