Open Source Invoicing Software

Why Open Source Invoicing Matters

Invoicing is one of the most critical workflows for service-based businesses and freelancers. Getting paid depends on sending clear, professional invoices promptly and following up on overdue payments consistently. Proprietary invoicing platforms like FreshBooks, Wave, and Zoho Invoice offer polished experiences, but they come with recurring costs that compound over time, particularly as you add features, users, or exceed invoice volume limits on free tiers.

Open source invoicing tools eliminate these subscription costs while providing comparable functionality. Self-hosting also means your client data, payment records, and business intelligence remain on infrastructure you control. For businesses operating in regulated industries or regions with strict data protection laws, this level of data ownership can be a compliance requirement rather than merely a preference.

The open source invoicing ecosystem has matured significantly. Modern platforms support customizable PDF invoice templates, automatic email delivery, online payment acceptance through multiple gateways, recurring invoice schedules, multi-currency billing, and client portals where customers can view their invoice history and make payments. These are not stripped-down alternatives to commercial tools. They are capable platforms backed by active development communities.

Invoice Ninja

Invoice Ninja is the most feature-rich open source invoicing platform available. Built with PHP (Laravel) and a React frontend, it provides a comprehensive invoicing and billing system that rivals commercial alternatives on functionality while remaining fully open source under the Elastic License.

The core feature set includes invoices, quotes, credits, purchase orders, and recurring invoices. Invoice templates are fully customizable with your branding, and the platform supports four built-in template designs with the ability to create custom designs using HTML and CSS. Invoices can be sent directly via email with integrated tracking that shows when a client opens the invoice.

Payment acceptance is a particular strength. Invoice Ninja integrates with over 40 payment gateways including Stripe, PayPal, Braintree, WePay, Authorize.net, and many others. Clients can pay directly from the invoice email or through a dedicated client portal, and partial payments are supported for milestone-based billing. The client portal also allows customers to view their complete invoice and payment history, download receipts, and manage their payment methods.

Additional features include expense tracking with receipt capture, project time tracking with the ability to convert tracked time directly into invoices, vendor management, bank connections for transaction import, and customizable workflows through automation rules. The platform supports over 30 languages and more than 100 currencies.

Invoice Ninja can be self-hosted using Docker or deployed manually on a PHP-capable server. Alternatively, the company offers a free hosted plan for up to 20 clients and a paid hosted plan for larger operations. The self-hosted version has no client or invoice limits.

Best for: freelancers, agencies, and small businesses whose primary need is professional invoicing with online payment acceptance, and who want the deepest invoicing feature set available in an open source platform.

Akaunting

Akaunting approaches invoicing as one component of a broader accounting workflow. When you create an invoice in Akaunting, the system automatically generates the corresponding journal entries in your general ledger, updates accounts receivable, and reflects the transaction in your financial reports. When you record payment against an invoice, the accounting entries are updated automatically. This integration eliminates the double-entry that occurs when invoicing and accounting run as separate systems.

The invoicing feature set includes customizable templates, email delivery, payment tracking with partial payment support, overdue payment reminders, and recurring invoice schedules. Client management lets you store contact details, billing addresses, and transaction history for each customer. The client portal allows customers to view and pay their invoices online when payment gateway apps are installed from the marketplace.

Where Akaunting differs from Invoice Ninja is scope. Akaunting handles invoicing, expense management, bill tracking, bank reconciliation, and financial reporting in a single platform. If you need both invoicing and accounting, Akaunting avoids the need to synchronize data between separate tools. If you primarily need invoicing and the accounting features are secondary, Invoice Ninja provides deeper invoicing functionality.

Best for: small businesses that want invoicing integrated directly into their accounting workflow so that creating invoices and recording payments automatically maintains accurate financial records.

InvoicePlane

InvoicePlane is a self-hosted invoicing application forked from the discontinued FusionInvoice project. Written in PHP using the CodeIgniter framework, it provides a straightforward invoicing workflow without the complexity of a full accounting platform.

Core features include invoice and quote creation, recurring invoices, custom fields for industry-specific data, PDF generation, and email delivery. The platform supports multiple tax rates, discount configurations, and product/service items that can be saved and reused across invoices. Client management includes contact details, notes, and custom fields for additional information.

InvoicePlane integrates with 25 online payment services for accepting payments through invoices. Multi-language support covers a wide range of languages, and multi-currency support handles international billing. The interface is functional and clean, though less polished than Invoice Ninja or Akaunting.

The project received a significant update with version 1.7.0, which added PHP 8.2+ compatibility and addressed security vulnerabilities including cross-site scripting fixes. Development has been community-driven since the fork, with active contributors maintaining the project on GitHub.

Best for: freelancers and sole proprietors who want a simple, lightweight invoicing tool without the overhead of a full accounting platform or the complexity of a feature-heavy invoicing system.

Crater

Crater is a relatively newer open source invoicing platform built with Laravel and VueJS. It positions itself as a modern alternative to Invoice Ninja and InvoicePlane, with a clean interface and a focus on the core invoicing workflow for freelancers and small businesses.

Features include invoicing, estimates, expense tracking, payment recording, tax management, and customizable invoice templates. The platform supports multiple currencies, custom fields, and item categories. A built-in reporting module provides revenue summaries and expense breakdowns.

Crater can be self-hosted on a standard LAMP/LEMP stack or deployed using Docker. The project also offers a mobile app for iOS and Android that syncs with your self-hosted instance, enabling invoice management on the go. The API supports integration with other business tools.

Best for: freelancers who want a modern, mobile-friendly invoicing platform with a clean design and straightforward feature set.

Key Features to Compare

When evaluating open source invoicing platforms, several features deserve particular attention based on their impact on daily workflow efficiency.

Recurring invoices automate billing for retainer agreements, subscription services, and regular maintenance contracts. All four platforms listed above support recurring invoices, but the configuration options vary. Invoice Ninja offers the most granular recurrence settings including auto-billing through saved payment methods.

Payment gateway integration determines how easily your clients can pay. Invoice Ninja leads with over 40 gateway integrations. Akaunting and InvoicePlane offer substantial gateway support through plugins and built-in integrations respectively. The more gateways available, the more payment options you can offer clients in different regions.

Client portals let your customers view their invoice history, download receipts, and make payments through a dedicated interface. Invoice Ninja and Akaunting both provide client portals, while InvoicePlane and Crater focus more on direct email-based invoicing without a dedicated portal.

Multi-currency support matters for businesses with international clients. All four platforms support multi-currency billing, but the depth varies. Invoice Ninja handles over 100 currencies with automatic exchange rate lookups. Akaunting provides solid multi-currency support integrated with its accounting module. Test the specific currency handling with your most common currencies before committing.

Customization and branding affect how professional your invoices look to clients. Invoice Ninja offers the most template customization with HTML/CSS-based design. Akaunting and Crater provide template builders with good branding options. InvoicePlane offers basic customization that covers essential branding needs.

Choosing Between Standalone Invoicing and Integrated Accounting

The fundamental decision is whether you need standalone invoicing or invoicing integrated into a broader accounting platform.

Choose a standalone invoicing tool like Invoice Ninja or InvoicePlane if invoicing is your primary financial workflow, you handle accounting separately (perhaps through a desktop tool like GnuCash or through your accountant), and you want the deepest possible invoicing feature set without the overhead of accounting modules you will not use.

Choose an integrated platform like Akaunting if you want invoicing, expense management, and financial reporting in a single system. The integration ensures that every invoice and payment automatically updates your books, eliminating reconciliation work and reducing errors from manual data entry between separate systems.

For businesses that start with standalone invoicing and later need accounting, Invoice Ninja provides basic expense tracking and reporting that may be sufficient. For those who need full accounting from the start, Akaunting provides the most seamless integration of invoicing into a complete accounting workflow.