Sandbox vs StopLight: What are the differences?
Sandbox: Quick and easy mock RESTful API and SOAP webservices. Quickly mock RESTful API or SOAP web-services with simple or dynamic responses, and fault injection to simulate real application behaviour; StopLight: Visual API Tooling. Stop writing thousands of lines of specification code. Our intuitive visual editors significantly cut down on design time, and are spec agnostic. Generate OAI (Swagger) and RAML specification code on demand.
Sandbox and StopLight can be categorized as "API" tools.
Sandbox is an open source tool with 161 GitHub stars and 28 GitHub forks. Here's a link to Sandbox's open source repository on GitHub.