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 Chrome OS. 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).
Humlix shows you an easy way of generating tests for your web APIs. All you need to do is create a test request using the test request builder within Humlix and give an example of how your endpoints look and what type of data they want.
RESTtest is a simple yet intuitive way to test RESTful web services and standard HTTP calls. RESTtest allows you to enter a HTTP request body and any necessary headers. After the request is submitted, response information can be both viewed and saved to disk.
APITree is a free cloud-based API tool to create, manage and share OpenAPI specifications. It converts your OpenApi v2 / v3 specification into a beautiful technical API documentation. Public API documentation is hosted for free.