I’m not sure I 100% understand your question. The REST API can be accessed by anything that send a properly formatted HTTP GET, POST, or DELETE. Describe what you are trying to achieve here. What is the “client” application? Are you driving automated testing?
The is an open source (and commercial) product called “Talend ESB” that provides a wide array of tools to make interacting with web services easier. However, it has a steep learning curve, though the documentation is decent. It is a component based programming paradigm with a GUI interface. The one thing it has is tools to help you parse and map output.