Source : https://solidinvoice.co/
Download :
Apache80 : https://www.myqnap.org/product/solidinvoice80/
Apache81 : https://www.myqnap.org/product/solidinvoice81/
SolidInvoice is a simple open source invoicing application aimed to help small businesses and freelancers manage their day-to-day billing. It's a feature rich elegant online application to ensure that you can always get paid on time.
Features :
Clients and Contacts management
Create and manage Quotes
Create and manage Invoices
Accept payments online
Tax and discount handling
RESTful API
Receive Notifications either via text message, email or through HipChat
More to come