Overview
Stock, sales and receipts in one desktop application, aimed at shops and pharmacies rather than at anything that assumes a permanent connection.
Complexities tackled
A sale touches several things at once. Recording a transaction has to decrement stock, produce a receipt and record the line items, and all of it has to happen or none of it. Getting that boundary right is what stops the inventory drifting away from reality over months of use.
Desktop because of where it runs. A shop counter with unreliable connectivity is not a good home for a web application. Building it as a desktop tool with a local database was the environment making the decision, not preference.
Stack
Java with a desktop interface, MySQL for storage.
Working on something similar?
Tell me what you are building and what is in the way. I will tell you honestly whether I am the right person for it.