From simple CRM, Bookkeeping packages and Office Suites to full-blown ERP systems, open source software can provide free options for small businesses that are lacking in budget for big-dollar enterprise applications.

 Microsoft's closed-source Windows operating system has by far the highest share of the PC client operating system market, followed in a distant second by Apple's Mac OS X. Linux and other wholly open source operating systems have only a tiny market share.

It's not hard to see why. Despite the advances made by distributions such as Ubuntu, desktop Linux is still miles behind Windows and OS X in terms of the look, the feel and the slickness that most office workers have come to expect. The vast majority of companies simply aren't prepared to make office workers use an open source OS — and most office workers aren't prepared to use them, either.

Even if you want to stick with a closed source operating system (or, the case of OS X, partially closed source), your business can still take advantage of a vast amount of open source software. The most attractive benefit of doing so: It's generally available to download and run for nothing. While support usually isn't available for such free software, it's frequently offered at an additional cost by the author or a third party. It may be included in a low-cost commercially licensed version as well.

Is it possible, then, to run a business entirely on software that can be downloaded for free? There certainly are many options that make it possible