Edit: The article was updated. Thanks to the replies from Martin Tournoij and Kellen Scarlett.
Web analytics applications
I had been using Google Analytics for a while. It's easy to setup. Just add a script and is ready to go. Then I checked out the open source alternatives. Matomo was originally based on Piwik, but Piwik Pro went commercial only and is not open source anymore. Matomo is open source and is written in PHP.