Rest client or Advanced Rest client or light weight rest client addons for firefox and chrom respectively. These addons provide validation, formatted output and many more other options.
Personally I prefer Chrome's Advanced Rest Client.
Firefox Addon - https://addons.mozilla.org/en-US/firefox/addon/restclient/
Chrome Addon - https://chrome.google.com/webstore/detail/advanced-rest-client/hgmloofddffdnphfgcellkdfbfbjeloo
Following jar is the desktop version rest client. Since it is a java application, we only need java installed on our machine. It is independent of the operating system. It also has command line utility to call your services from command prompt.