BillingEngine is a German online invoicing and bookkeeping software for freelancers, small businesses and tradespeople. It creates e-invoices in the ZUGFeRD and XRechnung formats (EN 16931), receives incoming e-invoices, archives all documents in a GoBD-compliant way and reads receipts with AI. Tax advisors get read-only access and export data in DATEV format. A free plan is available.