A free, open-source office productivity suite that can free users from the tyranny of Microsoft Office. Best of all, it is available for Windows, Linux, and Mac operating systems. It can store all data in an international open standard format, but it can also read and write files from other common office software packages. Its Writer word processing module can open Microsoft Word documents (.doc); its Calc spreadsheet can directly open Microsoft Excel spreadsheets (.xls); and its Impress presentation module can open Microsoft PowerPoint slide shows (.ppt).
While OpenOffice's data base module called Base cannot directly open or import Microsoft Access database files, it can link to Access tables. Users can then drop-and-drag the new links to a second Base document that creates independent, self-contained tables with the same end result as if you had imported the tables.
Not every Microsoft Office feature will have an exact counterpart in OpenOffice, but OpenOffice is an extremely powerful application suite in its own right. In fact, some tasks are easier in OpenOffice than in Microsoft Office. OpenOffice is a substantial download (greater than 120Mb), but it is well worth the effort.
Numerous add-on extensions are available for OpenOffice in much the same way as Mozilla's Firefox and Thunderbird. Here are a few of the ones I found most useful:
OpenOffice has a grammar checking framework, but does not come with a grammar checker. This extension provides that essential grammar checking capability. Note: after you install the extension, you will need to close OpenOffice entirely and then re-open it for the extension to take effect. [Added 19 December 2009]
In OpenOffice's database program called Base, reports are awkward to build and have limited capability. This extension adds significant flexibility and features on a par with Microsoft Access. If you have even the slightest inclination to generate reports with Base, this extension is an absolute must. [Added 19 December 2009]
These two packages contain over 120 templates for use in the business world. I categorize them as nice-to-have rather than must-haves because they lack certain essentials such as newsletters, résumés, and calendars, but they are worth installing nevertheless. [Added 19 December 2009]