Jes EÜR
1. Freelancing requirements in Germany
Being a freelancer in Germany is not as simple as being a freelancer in other parts of the world. It can be very complicated, especially for a beginner.
It is not enough to just start working and worry later about taxes, registration, and other legalities. No, you first need to register yourself with the tax office. Then you need to make clear whether you are Selbständig or Freiberufler. While both can be translated as freelancer, the obligations, legal requirements, and bookkeeping differ.
2. Anlage EÜR
Although freelancers are not required to do full double-entry accounting, like GMBH or UG, they are required to report their earnings at the end of the year in a consolidated way by submitting the so-called Anlage-EÜR to the tax office. Being a Freiberufler, one is theoretically not required to fill in the form, but I have heard all kinds of stories that tax officials don't like it when you make things more complicated for them, and not submitting Anlage-EÜR electronically is definitely more work for them.
3. Jes-EÜR
There are a lot of programs that allow one to do bookkeeping, most of them commercial, with varying quality and pricing. Working primarily on Linux, and not even owning a Windows machine, makes the choice much worse. Only a few commercially available software packages support non-Windows platforms, and non-Windows usually means Mac.
There are a couple of online software packages, but they always seemed a bit limited compared to the desktop versions. And I don't like the subscription model where I lose all data and convenience when I decide to stop paying for the service.
Then I came across Jes EÜR. It's a nice Java-based cross-platform program that allows you to track income and expenses, categorize them in the standard categories, and provide a report that can be used to submit Anlage-EÜR. Granted, it is missing an option to automatically submit it to the tax office, but it provides printouts with explanations that would make filling in the form on the official tax department website a two-minute effort. I even like it more that way, since it gives an impression of control during the process.