A basic PHP/MySQL/HTML Billing APP. Meant for developers learning.
Here is PHP/MySQL/HTML code that is a sample Entry Level Billing APP. It is Free, and mostly for learning purposes. You can install on a Windows or linux server, and look at the PHP code files on your PC.
LinxBooks – Have faith and carry on.
Overview
LinxBook is a simple and easy-to-use business accounting application. Linxbooks includes basic features that help the businesses create invoices, quotations, manage payments, payrolls, contracts and expenses
Download at GitHub: https://github.com/LinxHQ/linxbooks
Demo is at: http://linxbooks.com/demo (user: admin, password: admin123)
...We provide pay-per-use hosted invoicing solution, that is quick and easy for you to generate quotations and invoices. We're looking at improving it further, to deliver added values, other than basic features that has already offered. Visit us at http://L-invoice.com for more details.
Have fun with L-invoice, your quick and easy invoicing solution.