Sandbox is described as 'Accelerate application development
Quick and easy mock RESTful API and SOAP webservices. Generate from API definitions,
instant deploy, collaborative build, and debugging tools for integration' and is an website. There are more than 10 alternatives to Sandbox, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and SaaS apps. The best Sandbox alternative is soapUI, which is both free and Open Source. Other great sites and apps similar to Sandbox are AITable, Beeceptor, WireMock and MockServer.