Piwik provides default standard indicators: number of visitors, most viewed pages, average time, keywords used, geographical origin, login hours, …
The data can be downloaded in CSV, XML, PHP and Json.
The interface is user-friendly and the dashboard is customizable (by adding or removing widgets) to highlight your key indicators.
A demonstration site offers you to consult the different features offered: http://demo.piwik.org/
Licence: GNU General Public license
Online help, FAQ and forum: http://piwik.org/docs/