Google Analytics, the most popular and free analytics tool around, has already an API to pull data from.

OOcharts, a free service, adds a layer between you and the GA API to simplify and improve the requests you make.

First of all, a JS library allows you to get any data with a visualization using the Google Charts.

OOcharts

OOcharts also helps you stay within the limits of Google Analytics API by queuing and the requests.

And, a caching feature makes sure you get the results of similar requests much faster.

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