Google Analytics – the most popular and free analysis tool that is already equipped with an API to retrieve the data.
OOcharts is a free service that adds an extra layer between you and GA API, which simplifies and improves the requests you make.
First of all, JS-library allows you to get any data with visualization using Google Charts.
OOcharts also helps you not to go beyond Google Analytics API through requests and queues.
Besides, the caching mechanism can ensure a more rapid results in providing similar requests.