Mockoon is the easiest and quickest way to run mock REST API servers. No remote deployment, no account required, free, open source and cross-platform.

Use Postman's API client to create and save REST, SOAP, and GraphQL queries. Send requests, inspect responses, and easily debug APIs.

REST Assured Website

Fast, easy and reliable testing for integrating web apps, APIs and microservices

SoapUI is an automated testing tool for SOAP and REST APIs. Mostly replaced by Postman - useful if you prefer foss. Commercial version available