var request = new XMLHttpRequest();
request.open('POST', 'example.com', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
A guy named John Resig created the first release of jQuery in 2006. Nowadays, it is open source software meaning it is free to use and anyone can contribute to it’s codebase. It is actively worked on with version 3.1 being released in July 2016.
Find out more about jQuery at the jQuery Wikipedia article.