The main productivity suite used by individuals and businesses in the U.S. is Microsoft Office. This suite includes Word (writing documents), Excel (spreadsheets), Access (databases), and PowerPoint (presentations). They also have their lite version - Microsoft Works that comes pre-installed on many computers. Several competitors exist - for example Corel WordPerfect. But nobody nears the market share or dominance of Microsoft Office. And no one can deny that Microsoft Office is a good piece of software.
Sun Microsystems, a giant in the computing world that has played a large role in the development of computers and software but is much less known than similar companies like Microsoft or IBM created StarOffice, a competitive office suite to go against Microsoft Office and take away some of its dominance. They failed, so they decided to take any approach. They open sourced StarOffice and dedicated some programmers to its continued development. Other companies also interested in helping remove some of Microsoft's dominance began joining the effort, as well as individual programmers and the search behemoth - Google. Together they first released OpenOffice 1.0 - a half-way decent office suite that lacked a good database application. Within the past year or so they released 2.0. Now here was a real office suite.
I've been using OpenOffice for four or five years now as my primary word processor, at a mainly Microsoft Office college and then now in a mainly Microsoft world. With 2.0 OpenOffice really stepped up there game. No, it isn't Microsoft Office. The help documentation isn't as comprehensive. The functions aren't always as intuitive. And while it is able to read Microsoft documents decently well, some complex documents or formulas fail.
Still, if you are opening to trying new software or can't afford to shell out the $300-$400 that is Microsoft Office, then I recommend giving OpenOffice a try. It is being adopted by governments, businesses, and individuals around the world. Both Novell and Sun Microsystems utilize OpenOffice as their main office suite.
In case you are wondering. OpenOffice has Writer for creating documents (similar to Word), Impress for presentations (similar to PowerPoint), Base for creating databases (similar to Access), and Calc for spreadsheets (similar to Excel). It also includes a mathematical formulas and drawing program - though I have not utilized either of these programs besides opening them up and fooling around.