Google Analytics is a free web analytics solution provided by Google, featuring several client-side APIs, as well as REST APIs for data export and for management.
Google Analytics is a service offered by Google that generates detailed statistics about a website's traffic and traffic sources and measures conversions and sales. The product is aimed at marketers as opposed to webmasters and technologists from which the industry of web analytics originally grew. It's the most widely used website statistics service.
The basic service is free of charge and a premium version is available for a fee.
Google Analytics can track visitors from all referrers, including search engines and social networks, direct visits and referring sites. It also displays advertising, pay-per-click networks, email marketing and digital collateral such as links within PDF documents.
APIs that are part of Google Analytics
Collection APIs & SDKs
These libraries that can be used by website developers/webmasters or mobile app developers to track user interaction data and send it to Google Analytics.
Can be used to retrieve all management information on Google Analytics: Users, Profiles, Goals, Filters, etc.
The reporting APIs can be used to retrieve report data that is present on the Google Analytics interface.
Universal Analytics Upgrade Center
Information on upgrading to Universal Analytics, a set of features that change the way data is collected and organized in your Google Analytics account.
Google provides some playground-like tools to let you play and learn the APIs: