The second most popular source code that I have ever written so far is my Point of Sale.
This program has the following features.
1. Barcode support
2. Point of Sales
3. Place an order (sales order or purchase order)
4. Receive or deliver an order by batch
5. Support for returning of orders
6. Product inventory according to unit of measures
Run the source code to appreciate the program.
Because of this source code I also received a lot of project all over the world. This is the price of being a generous programmer sometimes. We do not know that the return is more than what we give.
I never ever thought that because of sharing my source code I will receive a lot of opportunities. Not only that I can help my fellow programmer but I can also earn money through this.
Here's the link for the source code.