Rechnung+ is a free web-tool for keeping track of the time spent on some work and making bills for it. It is completely free to use. It allows you to make invoices for any subset of the work entered in the system. The calculation of the bills total time and money (taking care of VAT) will be done automatically. The invoices can be printed or saved into PDFs. A powerful statistical report generator will help you to analyze the work you did.

Note: This app requires registration which can be done at the main site here. Try with TestiPhone