Postman vs Sandbox: What are the differences?
Developers describe Postman as "Only complete API development environment". Postman is the only complete API development environment, used by nearly five million developers and more than 100,000 companies worldwide. On the other hand, Sandbox is detailed as "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.
Postman and Sandbox 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.