Google Site Search is a refined and paying version of the free Google Custom Search service. Google Site Search was previously also offered under the name: Google Custom Search Business Edition.
For both solutions, the search results can be sent to the site via an XML API interface where the Custom Search results are automatically displayed in the Look & Feel of the site. In the case of Google Site Search, they are shown by default in Google Look & Feel, but it is possible to match the Look & Feel of your website. That's also the main reason why kañooh works with these types of Google Search solutions.