Microsoft Office 2010 takes on all comers
OpenOffice.org, LibreOffice, IBM Lotus Symphony, SoftMaker Office, Corel WordPerfect, and Google Docs challenge the Microsoft juggernautFollow @syegulalp
OpenOffice.org's word processor, Writer, most closely resembles Microsoft Word from (again) 2003 or so. What's interesting is how despite the older look and feel, a few of Writer's features predate similar items found in current versions of Word. Example: The export-to-PDF function, which has many more options (security, user-interface settings) than Word 2010's own native exporter. Many of the document handling functions -- for example, the treatment of sections, subdocuments, styles, and formatting -- are on a par with Word.
Especially interesting is the word-completion function. Words longer than 10 letters (this value is customizable) are automatically collected in a list. If you start to type something that OpenOffice.org thinks is one of those words, it offers a suggestion. Press Enter to apply the suggestion or continue typing to ignore it. I found it annoying at first because it wasn't trained for my word choices, but over time -- and in longer, particularly verbose documents -- it became quite useful. Naturally, this whole feature can be disabled if you don't like it.
The real shortcomings, for me, are in the grammar and spelling tools. The built-in thesaurus and spell-checker aren't bad, but there's nothing here on the level of Microsoft Word's context-sensitive spelling and grammar checking system. Also, OpenOffice.org doesn't have a native grammar-checking mechanism; grammar-checking tools need to be plugged in through the program's add-on system. To that end, the most commonly used grammar add-on for OpenOffice.org, LanguageTool, is available as a download, but its trapping of language issues is spotty. Some obvious mistakes, like blatant sentence fragments, slide right through, while other legitimate uses of language are flagged; for example, the term "cant," meaning jargon or insincere talk, is assumed to be "can't." Those weaned on Word's grammar tools may find this a major step down, as I did.
The other major shortcoming is what happens to Microsoft-format documents after they're edited in OpenOffice.org and passed back to the original user. The older .doc format is preserved more or less intact, but the newer .docx format is not handled nearly as well.
The spreadsheet application, Calc, uses the OASIS OpenFormula standard for its formulas rather than Excel's own. That said, someone with Excel experience sitting down with Calc shouldn't have too much trouble -- many common functions, such as SUM(), are identical across both programs. What's trickier is when you use existing Excel documents in Calc. The more sophisticated the spreadsheet, the less likely it is to open or function correctly. A fairly complex home-mortgage calculator only partly worked (the graph in the middle of the sheet didn't display or auto-update), although my own home-expense spreadsheets with minimal formulas work fine.
For most people (me included) Impress, the presentation app, will work as a drop-in replacement for PowerPoint. The vast majority of the essential features you'd expect to find in a presentation program are all here: transitions, master-page formats for slides, the ability to show presentations on one display and read your own notes on another, a handout-page designer, and -- most useful -- exporting to HTML with a variety of presentation options. Again, the main caveat here is how well the program opens and displays existing presentations created in PowerPoint. The more complex the presentation, the more likely it is to display incorrectly. Here again, try opening some existing .ppt/.pptx files before you commit to anything. Also, some presentations that didn't import correctly as .pptx files worked fine -- including animation and transitions -- when resaved from Office 2010 into .ppt format and imported into OpenOffice.org.
OpenOffice.org comes in a variety of packages and alternative editions, such as the PortableApps version that can be run from a flash drive or external hard drive without needing to be formally installed. Installing OpenOffice.org across a Windows-centric organization will require some heavy lifting. The OpenOffice.org wiki has some documentation on how to do this, but it hasn't been updated since version 2.x; a thread in the OpenOffice.org support forums talks about how to deploy 3.x across Windows machines.
OpenOffice.org's spelling and grammar tools come in a distant second to Microsoft Office, although the rest of the program sports useful features.