billing app4 flutter pos2 inventory management2 invoice2 offline pos2 shop management2 accounting app1 accounting system1 barcode scanner1 billing invoice1 business management1 cashier1 client management1 cross platform1 dark mode1 estimate maker1 expense tracker1 flutter app1 flutter invoice app1 flutter template1 hive database1 inventory1 invoice app1 invoice generator1 invoice maker1 invoice manager1 invoicer1 invoices1 invoices generator app1 invoicing1