Simple Invoices & Estimates is described as 'A simple, easy to use Invoices & Estimates program for Windows® Computers. It supports unlimited companies, adding on the fly items, customer list, items list, and easy to understand invoices report. Great for everyday businesses' and is an app in the Business & Commerce category. There are more than 100 alternatives to Simple Invoices & Estimates for a variety of platforms, including Online / Web-based, Windows, Mac, iPhone and Linux. The best alternative is GnuCash, which is both free and Open Source. Other great apps like Simple Invoices & Estimates are Odoo (Freemium, Open Source), HomeBank (Free, Open Source), ERPNext (Free, Open Source) and Wave (Free).
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.
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.
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.
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.
Manager is free accounting software for Windows, Mac and Linux. It features an intuitive and innovative user interface with modules such as cashbook, invoicing, receivables, payables, taxes and comprehensive financial reports.
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.