The best open source alternative to Xero is GnuCash, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Xero and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Xero are ERPNext (Free, Open Source), Odoo (Freemium, Open Source), Dolibarr (Free, Open Source) and Invoice Ninja (Freemium, Open Source).
ERPNext is a free and open-source integrated Enterprise Resource Planning (ERP) software developed by Frappé Technologies Pvt. Ltd. and is built on MariaDB database system using a Python based server-side framework.
Odoo (formerly OpenERP) is a suite of open-source business apps written in Python and distributed under the AGPL license, under the Open Core software business model. It is used by 2 million users worldwide to manage companies of all size.
Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line. This may put off some users, since there is no flashy UI, but for those who want unparalleled reporting access to their data there are few alternatives.
From invoicing to expense tracking to accounting, Akaunting has all the tools you need to manage your money online, for free. That's right, completely free. There is no limited or trial version. No hidden charges or setup fees.
inoERP is an open source php based enterprise management system. The ERP systems contain all the required modules for running any small to mid-size businesses. The features are very similar to Oracle R12/ Fusion Application and SAP.
webERP is a complete web based accounting/ERP system that requires only a web-browser and pdf reader to use. It has a wide range of features suitable for many businesses particularly distributed businesses in wholesale and distribution.