RESTClient - RESTClient can be used to test variety of HTTP communications and RESTful webservices.
Postman - The Collaboration Platform for API Development
Requester - HTTP client plugin for Sublime Text with an expansive feature set, modern UX, elegant syntax and...
Hurl.it - Hurl makes HTTP requests.
Insomnia REST - The most intuitive cross-platform REST API Client ð´
Cocoa Rest Client - A free open source, native Apple OS X app for testing HTTP/REST endpoints