From GSA:

The GSA Buchhalter is a software for all self-employed persons and small companies who do not need a double entry bookkeeping. The program is easy to use and is not overloaded with unnecessary functions. The application can manage unlimited entries of your customers and their in- and outcomes. The booking accounts are freely configurable and each of them can be changed at every time. You get an immediate overview of all bookings in a graphical diagram. The time period in this overview is changeable to monthly, yearly or to a free date. Moreover the accountant program contains an income surplus calculator and a monthly value added tax report. You have tax reports included for the tax office (sales tax report and statement on excess of receipts over expenses). For your safety we have included the possibility to quickly make backups of the database and of course the ability to write it back in case of an emergency