Invoice Ninja is described as 'Free, open-source invoicing tool with PDF generation, online payment support, invoice templates, multi-gateway integration, and business customization options' and is a Time Tracking tool in the business & commerce category. There are more than 100 alternatives to Invoice Ninja for a variety of platforms, including Web-based, iPhone, SaaS, Mac and Windows apps. The best Invoice Ninja alternative is Summit Finance, which is both free and Open Source. Other great apps like Invoice Ninja are Midday, Cattr, Clockify and InvoicePlane.