I often get web traffic on my blog from those who are curious about the German educational system. I wrote a piece about the primary and secondary school system, but I wouldn't be surprised if people were more interested in knowing about free university.
It is true that as of now, German universities are free for qualified individuals, whether or not those individuals are German or members of the European Union. International media, especially American sources, has been blowing up lately with stories about free tuition. However, the key word for prospective students is qualified; it's not just a free-for-all for those who haven't done well in school.
Also, one might think that the student wouldn't need to have any money. There are no tuition fees, so that must be true, right? No, that's wrong. Foreign students must show that they have the money, up front, to be able to afford living expenses for one year.
Depending on one's program and level of study, one also must be quite fluent in German. Some master's programs don't require it but for lower-level classes, it's a must.
There is a ton more to studying in Germany and I don't have that experience. I asked two of my friends, one who is a university lecturer and the other who is a native German and PhD student. I couldn't keep up with notes or the barrage of (helpful) information they were imparting so I'll point to some articles of interest. For those who'd like to go to a German uni, I'd suggest conducting a ton more research.
You Can Now Go to College in Germany for Free, No Matter Where You’re From by Rebecca Schuman.
A reddit post about studying in Germany as an undergraduate; my PhD student friend recommended it and says that it is accurate according to his experience.