Despite the wealth of free applications out there, many small business owners continue to spend an inordinate amount of their all-too-scarce resources on software. Microsoft Office 2010? That'll be $499.99--or $279.99 if you can do without the Professional version. QuickBooks 2010? $159.95 or more. Adobe PhotoShop CS5? A whopping $699.

The good news is that there are free and open-source alternatives for virtually every package a small business might need, and most of them are excellent. Whether or not you've already made the switch to Linux -- there are, after all, myriad security and other reasons for doing so -- these free apps can be just what any small business needs to succeed.

1. Office Productivity: OpenOffice

OpenOffice.org 3 (also known as OO.o) is a fantastic open-source alternative to Microsoft Office. With components for word processing, spreadsheets, presentations, graphics, databases and more, it is available in many languages and works on all common operating systems, including Linux, Mac and Windows. All data gets stored in an international open standard format, and the software can read and write files from Office as well. Perhaps best of all, the interface is so familiar and intuitive that you might not even realize you're using anything new. You can download and use OpenOffice free of charge.

2. Accounting: GnuCash

GnuCash is a personal and small-business financial-accounting software package that's also available for Linux, Mac OS X, and Windows. Both powerful and flexible, GnuCash lets you track bank accounts, stocks, income and expenses. As quick and intuitive to use as a checkbook register, it is based on professional accounting principles to ensure balanced books and accurate reports. Among GnuCash's key features are double-entry accounting, small-business accounting, invoicing and more. Data can be imported from programs such as Microsoft Money and Quicken, while it can be exported to spreadsheets such as Microsoft Excel. Once again, this free software's interface is so intuitive and familiar that if you've used other accounting programs before, this one will be no problem.

3. Desktop publishing: Scribus

Scribus is a free program that offers professional page-layout capabilities for Linux, Mac OSX and Windows desktops. Scribus supports professional publishing features including CMYK color separations for both press-ready output and PDF creation. I've found the software can do just about anything the paid packages can, and it's comparable to InDesign or Publisher, for instance.

4. E-mail: Zimbra

Zimbra Desktop is free e-mail and calendar software that runs on any Linux, Mac or Windows computer. The tool offers e-mail, contacts, calendar and document capabilities all in one application, and it lets users read e-mail from any POP or IMAP e-mail account, including Gmail, Hotmail or business e-mail. Owned by VMware, Zimbra works both online and off, and there's no limit to the size of your e-mail storage. As an added bonus, it's also available in 20 languages.

5. Web page editing: KompoZer

Much like Microsoft's old FrontPage, KompoZer is a tool for anyone who ever works with a Web page. Downloadable for free and compatible with Linux as well as the usual other alternatives, KompoZer is a WYSIWYG (What You See Is What You Get) editor, meaning that you can edit Web pages visually as well as by working with the raw HTML code. The free software is extremely easy to use, making it ideal for nontechnical computer users who want to create an attractive, professional-looking Web site without necessarily needing to know HTML.

6. Graphics: GIMP

GIMP, which stands for "GNU Image Manipulation Program," is a free and open source alternative to Adobe's pricey PhotoShop product. With an interface very similar to PhotoShop's, GIMP offers capabilities including photo retouching, image composition and image authoring. I believe GIMP will satisfy all but the highest-end professional graphic designers. It's perfect for making Web graphics, retouching product photos and creating marketing materials, and any images created can be saved in an array of common formats, including PSD Photoshop.

7. Backup: Amanda

Amanda is a backup and recovery solution that lets you set up a single master backup server to back up multiple hosts to a single large-capacity tape or disk drive. The software can back up a large number of workstations running multiple versions of Linux, Mac OS or Windows. Currently, it's used to protect more than half a million servers and desktops around the world. A sister service to Amanda, meanwhile, is Zmanda, which provides paid backup in the cloud.

8. HR management: OrangeHRM

OrangeHRM is a free package for human resources management. With modules for personnel information management, benefits, recruitment, employee self-service, leave, and time and attendance‚ the software also offers optional paid services including training, support and customization.

9. E-mail campaigns: phpList

If your business runs e-mail campaigns, phpList can be a great tool. The software is free to download, install and use, and it's easy to integrate with any Website. Ideal for newsletters, publicity lists, notifications and many other uses, phpList is designed to manage mailing lists with up to hundreds of thousands of subscribers. A Web interface lets you write and send messages and manage phpList over the internet.

10. Project management: OpenProj

OpenProj is a free project-management package that substitutes nicely for Microsoft Project but works with Linux and Mac as well as Windows. With more than a million users, OpenProj's installed base is second only to that of Microsoft Project itself--which, of course, costs a heck of a lot more. Gantt charts, PERT charts and all the other capabilities offered by Microsoft's software are in OpenProj as well, and existing Project files can be easily imported.

11. Antivirus: ClamAV

Even if you're running Linux, it's still a good idea to use some kind of antivirus software. Originally designed for Unix, ClamAV is a nice package that's now available for Linux as well as for Windows and a number of other platforms. The tool offers built-in support for almost all mail file formats as well as popular document formats including Microsoft Office, HTML, RTF and PDF. With a virus database that's updated multiple times per day, ClamAV is, of course, also free.