example with source code you can see https://github.com/usermicrodevices/prod-flet
application supports all major operating systems: Linux, Windows, MacOS, iOS, Android. The graphical user interface is built on the principle of filling the customer's basket, but in reality it is a cash register software that performs all mathematical calculations of the POS terminal. Product search is possible in the mode of typing from the keyboard or scanning with a connected scanner. The mobile version also contains a built-in barcode and QR code scanner - so it is possible to use a phone or tablet as a data collection terminal. After synchronizing the directories with the server, the application can work autonomously. Synchronization of directories is configured in selected time intervals. Sending sales and order data to the server can also be delayed in case of network breaks and is configured in selected time intervals. Trading equipment can be integrated through device drivers. An example of connecting trade scales can be found in the open source project. Banking and fiscal equipment can also be integrated through the appropriate drivers from manufacturers. Entering balances to control stocks (inventory management) in a warehouse or retail outlet from the application is done through an order and in the server admin panel it is changed to the appropriate document type with the appropriate counterparty.