Need a window application where a businessman can generate their bills. Along with that it should support similar application for multiple businessmen. With an admin panel to manage the inventory

I'm looking to develop a window application that will function as a billing system for a small businesses, as well as support similar applications for multiple businesses simultaneously. The system should support both online and offline billing structures, and it should include an admin panel that will be used for inventory management. This software is meant to be used by up to three businessmen. If you have experience in developing professional billing systems for small businesses, we'd love to hear from you!