FacturaRapida is a free, MIT-licensed invoicing tool for Spanish small businesses. One Python file, zero dependencies, runs 100% offline: it validates your client DNI/CIF with checksum, calculates Spanish VAT (21/10/4/0 percent) and totals in Spanish format, and generates a clean A4 invoice you save as PDF from the browser. No cloud, no subscription, no data ever leaves your machine: install Python, run one command, done. Commercial support edition on Payhip.
