Simple Invoicing is a php-based web app to manage your invoices/payments/quotations/customers. You can call this an open & responsive invoice management solution.
The user Interface is very easy and simple. There are 2 user levels, admins and sales. Reports including Daily Sales, Monthly Sales, and Custom search invoice/payment reports.
demo url: http://demo.saenterprises.ind.in/apcrm/
Admin login Detail: