I need to create a specialized analytics app based on Piwik, it will be a commercial SaaS service for small businesses. It uses the piwik javascript tracker, API and the DB to store events, custom variables etc.. just like piwik and extra functionality built on top. I'm just not sure if Piwik license allows it.
If you distribute a modified version of Piwik, or software that includes Piwik as a module, or develop a website for a customer/client that integrates closely with Piwik, you must give access to the code source and publish all the code under the GPL.
However, it also states:
The data coming from the Piwik API belongs to you and is not covered by the GPL.
You can use Piwik as a service, and reuse, publish, display, modify, process the data coming from the Piwik API using the REST API web services call.
.. so does that mean If I use Piwik Tracker, APIs and the database, but NOT its front-end admin panel, then GPL doesn't apply to me?