RESTClient is described as 'can be used to test variety of HTTP communications and RESTful webservices. Friendly GUI, rich functionalities' and is a HTTP Client in the category. There are more than 50 alternatives to RESTClient for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and SaaS. The best alternative is Wget, which is both free and Open Source. Other great apps like RESTClient are Insomnia REST Client (Freemium, Open Source), Postman (Freemium), cURL (Free, Open Source) and Paw (Paid).
GNU Wget is a free software package for retrieving files using HTTP(S) and FTP, the most widely-used Internet protocols. It is a non-interactive command line tool, so it may easily be called from scripts, cron jobs, terminals without X-Windows support, etc.
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.
cURL is a computer software project providing a library and command-line tool for transferring data using various protocols with URL syntax: supporting FTP, FTPS, SCP, SFTP, HTTP, HTTPS, TFTP, TELNET, DICT, LDAP, LDAPS and FILE.
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.