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Best Free Open Source Invoice Software

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Last editedOct 20222 min read

If you’re like most business owners, you’re always looking for ways to boost efficiency – particularly when it comes to getting paid. An efficient invoicing system reduces the need to chase up on late payments. Open source invoicing software cuts out unnecessary admin, saving time and money. In this guide, we’ll list the best free open source invoice software, allowing you to find the best fit.

What is free open source invoice software?

To begin with, it’s helpful to understand what makes open source software special. An open source system offers public source code, enabling any individual or business to modify the code to meet their own needs. This lends flexibility to the software because you can tweak the code to add unique features or fix bugs. There are varying levels of openness; in some cases you can modify the full source code, and in others only certain aspects are public. Free open source invoice software is also free to use, without monthly fees.

What are the benefits of free open source invoice software?

Here are just a few reasons why you should consider using open source invoice software:

  • Security: It might seem like open source code would be less secure, but in fact most of this type of software offers an added layer of security due to its public accessibility. Because the public can review the code for bugs and glitches, this helps reduce errors.

  • Affordability: You won’t be locked into a costly monthly subscription to access your accounting software. Instead, you’ll only need to think about development and maintenance.

  • Flexibility: You can modify the fully accessible source code in the way that best suits your business. Take the code as is, or customise it to integrate smoothly with your existing systems.

Best free open source invoice software

There’s a vast selection of free open source invoice software on the market today. Here are a few of the most accessible, feature-rich options for UK small businesses.


This billing software is free of charge at the basic level. It’s designed to manage all facets of the subscription billing process, including invoicing and payment collection. Chargebee offers a variety of open source projects, including a fully customisable customer portal, open source Ruby Gem, and Laravel package. One of the benefits of using Chargebee is that you can start out with hosted page integration before transitioning to using the system API.


If you’re looking for powerful free accounting and invoicing software, Crunch is a good option with no hidden fees or trial periods involved. It’s suitable for freelancers, sole traders, and limited companies with real-time finance management as well as invoicing. Users can send out unlimited free invoices, with a mobile-friendly app to track them on the go. Crunch has shifted over to a microservice based architecture running on Kubernetes, rebuilding its public API for independent developers to access freely.

Kill Bill

As its name suggests, Kill Bill helps businesses tackle everything related to billing. You’ll be able to manage invoices, customer databases, payments, and subscription services with plenty of customisation potential. The Kill Bill software is built using Ruby, requiring several Ruby Gems to function. Add custom plug-ins and create unique billing workflows for each client. Kill Bill also includes Java and HTTP REST APIs you can integrate with additional applications.

Invoice Ninja

Invoice Ninja is an open source invoicing system offering a high volume of free features, including customer support to help your business get off the ground. Add ‘buy now’ buttons to your website and emails, customise invoices with your company logo, and track payments as they come in. The software allows you to add up to 20 users with varying levels of permission, attaching documents and creating instant price quotes.

A good payment collection process goes hand in hand with invoicing. GoCardless integrates with over 350 partners, including free software like Chargebee and Crunch as well as popular accounting tools like Xero and QuickBooks. Create and issue invoices while collecting payment directly from customer bank accounts for a streamlined, efficient workflow.

We can help

GoCardless is a global payments solution that helps you automate payment collection, cutting down on the amount of financial admin your team needs to deal with. Find out how GoCardless can help you with one-off or recurring payments.

Over 85,000 businesses use GoCardless to get paid on time. Learn more about how you can improve payment processing at your business today.

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Interested in automating the way you get paid? GoCardless can help
Interested in automating the way you get paid? GoCardless can help

Interested in automating the way you get paid? GoCardless can help

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