I have been using Piwik for a couple of months and I love it.

I started using it first at my internship at leadelephant.com, not really as an analytics tool, but more as a data collection tool.

The main goal of Piwik is an analytics tool, a direct competitor to Google Analytics. But it's really more than that. Like the data collection method I just mentioned, it could also be a community monitoring tool, which is how we use it at  Habbies.nl.

Piwik is a JavaScript tracking snippet backed by a PHP dashboard and MySQL backend. Installation is really simple and it works out of the box. If you're site is having a thousand visitors a day it's a good idea to read through the Optimization docs.
If you're using Cloudflare, you might want to tweak the config file to start using X-FORWARDED-FOR headers.
Other than that it's just a quick install and you're done!

Piwik underwent a big redesign in 2014 and is looking quite good. (It used to look a little dated!)

I run both Google Analytics and Piwik. I use Piwik daily, to check up on real-time visitors and trends. I use Google Analytics for end-of-the-month kind of actions, looking at the aggregated data. There are a lot of blogposts already comparing GA with Piwik, but as you can see, you don't have to pick one.

You can use both!

So take 5 minutes out of your day and download and install Piwik.