Invoice Expert is a free Invoice, Inventory and Billing Software for small and medium businesses for Windows PC. Read Invoice Expert review here.

As with most of the best free invoicing software, Invoice Ninja lets you use payment gateways, such as WePay, Stripe, Authorize.net and PayPal.

The best free invoicing software includes Invoice Ninja, Wave Invoicing, Zoho Invoice, PayPal Invoicing, Square Invoices, Hiveage, Harvest and Hopscotch.