Open Source Point of Sale has a Customer Management module included:
It can be very useful to capture Customer Information while selling your products and services.
From the Sales Register, you can Select a Customer or Create a New one.
From the Customers tab, you can manage your Customers. For instance, you have quick access to their contact information, including their email addresses and phone numbers.
You can quickly email a customer by clicking on their email. You can email multiple customers by checking the checkbox next to their names and then clicking the "E-Mail" button. This lets you stay in contact with your best customers.
The system also has excellent Customer Reporting. For instance, you can print off a graphical Customer Summary Report that shows you which customers generated the most revenue for your store. You can drill down by Date Range and Sales Type to get more specific information.
You can also run a Customer Summary Report that lets you see how much you've sold and how much profit you've made off each customer. You can sort this information right in OSPOS or you can export it to Excel.
Finally, you have Detailed Customer Reports. These let you run off detailed sales reports for a specific customer. You can also export this information to Excel where you can work with it there.