From add-on to platform

The first version of rechnungs.tools worked because it was close to the spreadsheet. The rewrite was necessary because invoice work eventually needs more structure than a sheet can comfortably provide.

Multi-client support was one example. Many freelancers and small operators need to send invoices for more than one business context, and many simple tools make that awkward.

The platform version keeps the original promise - free invoice writing - but adds stronger document handling, more flexible client data, and support for formats such as ZUGFeRD.

The product direction is still deliberately narrow: make writing invoices simple, keep the free path useful, and only add structure where it removes real work.