This free version has the limitation that can not print documents. Otherwise it is fully operational. Part of the ads, can serve as a working agenda to schedule daily tasks or assignments.
It also serves to record the materials and labor that go into each job using're doing, avoiding oversights of materials and keeping track of the invoice amount to the extent that each job is.
Although you can not print from the terminal, you automatically calculates the invoice of your work. To issue it, just rewrite it in an editor.
They can be issued tickets and invoices from a portable minimpresora in the paid version.
The program has a twin brother who works on Windows (R), with which you can synchronize. (You can download it https://www.jmms.es.)