If you run a small or medium businesses you are probably operating on a shoestring budget and don't have the resources to purchase expensive enterprise software systems. But just because you don't have the money does not mean that you don't need the functionality that these systems provide.
Thankfully, the Open Source Software movement has developed some incredible, enterprise quality tools to help your business operate efficiently and effectively while staying on budget.
Accounting
Accounting is the most basic need of any business. You need a system that adheres 
to GAAP, provides robust reporting tools and still leaves some money left to be accounted for.
GnuCash
GnuCash is the QuickBooks of the open source world. It is simple to use, can import data from your bank in QuickBooks format and can generate most reports you will need. The downside is that it is a single user system, so if you have more than a couple of people handling accounting in your company, you may want to take a look at the next section.
Enterprise Resource Planning (ERP)
ERP systems integrate accounting, CRM, HRM, inventory management, supply chain management and they will make your morning coffee, too. These systems are meant to be one stop shops for almost any functions that your business will need.
Compiere
CompiereERP is a Java based application that is available in a free Community Edition as well as paid/supported versions. You can download, install and use this incredibly powerful ERP application at no cost to get started and then migrate to a commercially supported version as your business grows.OpenERP
OpenERP is also available in both free and commercial versions. Many of the features and functions in OpenERP migrate to the community edition after the developers recoup their initial investment from paid clients. This is another great application to consider as a starting point for your business. It is web based and can be installed and accessed by anyone on your team.
WebERP
WebERP is a more traditional Open Source application. It is a freely available download and completely web based. Support is available through the mailing lists that they can be read online via Nabble. Commercial support is available from a number of third parties, but the webERP developers do not sell commercial support as part of the product.
Human Resources
If you have more than a couple of employees, it can be very helpful to have software that tracks hours, 
vacation time, benefits and even provides an employee self service portal to reduce the amount of time you spend handling routine questions.
OrangeHRM
OrangeHRM seems to be the sole option in this arena. Thankfully it is full featured, covering just about every aspect of managing employees on a daily basis. You can purchase support and even contract with the developers for customization, but you can download and install the software at no cost to get yourself started.
Office Software
We all use common office applications day in and day out. Functions like word processing, spreadsheets and presentation creation are part of our daily workflow. Microsoft's Office suite can cost as much as $279.00, but you can get all of that functionality at no cost using these high quality open source alternatives.
OpenOffice
OpenOffice is the premier open source office application suite. It provides the digital trinity of word processing, spreadsheets and presentation creation, but it can do much more. Plugins add collaboration tools, alternative language dictionaries and database tools. It has solid support for importing and exporting Microsoft Office file formats so you can collaborate with your customers and colleagues and they won't know the difference.
KOffice
KOffice is another popular open source application that can handle your daily office needs. It has the expected word processing/spreadsheet/presentation trio, but extensions are available that add project management, flowchart creation and drawing features. The MS Office export functionality is not quite as robust as the support of OpenOffice but for the basic office tasks most of us perform, it is a great free tool.
Google Docs
Google Docs is a completely web based office suite. It has the same trio of applications available and all you need is a GMail account to get started. Collaboration tools set this suite apart from its competitors. You can share documents and folders with other users and everyone can edit and markup the documents. Final documents can be exported to MS Office formats, but the fidelity of the output is not perfect. It is a great fit if collaboration and free are your keywords.
EMail Applications
It doesn't seem to matter how many social networking apps and messaging services appear on the scene, we still use email as the main mode of communication for our businesses. While Outlook/Outlook Express are the most commonly used email clients in use, they are by no means the only ones available. The open source community has created a couple of top tier alternatives that are worth taking a look at.
