RESTer is described as 'A REST client for almost any web service (Firefox and Chrome extension)' and is an app in the Web Browsers category. There are more than 25 alternatives to RESTer for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and SaaS. The best alternative is Insomnia REST Client, which is both free and Open Source. Other great apps like RESTer are Postman (Freemium), HTTPie (Free, Open Source), Paw (Paid) and Hoppscotch (Free, Open Source).
Postman is a tool that facilitates the development and use of APIs. Postman provides all the functionality needed to create or simulate API specifications and use the Postman Collection Runner to create tests.
Easily craft your HTTP requests, try them, archive them. Setup HTTP Headers, URL parameters, form-encoded POST key-values or text. Get easy-to-read responses with well formatted headers and body. Sync your projects with your team through Paw for Teams.