MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
HttpMaster - HttpMaster is a professional software tool for testing and debugging HTTP applications, primarily aimed at REST API applications and web services.
Bearer - Bearer is an open source, fast and accurate static application security testing (SAST) tool that analyze your source code to discover, filter and prioritize security and privacy risks.
Request inspector - Debug web hooks, http clients
RestCase - Secure REST API Rapid Development Platform
Hoppscotch - Open source API development ecosystem