OpenOffice.org (also known as OOo or OO.o) is the most popular open source office suite (over 100 million downloads) with 14% of the large enterprise market and 19% of the small to mid-size business market. Founded by Sun Microsystems in 2000, OpenOffice was released in on May 2nd, 2002.
OpenOffice is actively supported by a large number of contributors and developers (see http://www.oooforum.org/ ) and by large corporations such as Sun Microsystems, IBM, Google and CollabNet.

Structure

OpenOffice.org consists of 6 applications, similar to Microsoft Office's structure:

• Writer - a word processor packed with lots of features like AutoCorrect, AutoComplete, AutoFormat,
• Calc - spreadsheets applications with tools for calculating, analyzing and presenting data in numerical reports
• Impress - tool for creating multimedia presentations, similar to Microsoft's PowerPoint
• Draw - software application for designing everything from 3D illustrations to diagrams
• Base - similar to Microsoft's Access, Base is used for creating and modifying databases (reports, tables, queries and forms);
• Math - tool for creating and managing maths equations.

You can also download an OpenOffice.org 2.x and Microsoft Office 2007 Feature Comparison here .

Download

Download the full OpenOffice.org suite of programs from here: http://download.openoffice.org/

For all your documents

WRITER has everything you would expect from a modern, fully equipped word processor or desktop publisher.

It's simple enough for a quick memo, powerful enough to create complete books with contents, diagrams, indexes, etc. You're free to concentrate on your message - while WRITER makes it look great. About the only downside is that things can go a little pear shaped when dealing with Microsoft Office documents containing heavy formatting, tables and suchlike.

WRITER behaves like MS Word, and it can also open and save word files. So it's great for sending to people who are still locked into Microsoft products.

The all-purpose spreadsheet

CALC is the spreadsheet program you've always wanted. Newcomers find it intuitive and easy to learn; professional data miners and number crunchers will appreciate the comprehensive range of advanced functions.

Save your spreadsheets in OpenDocument format, the new international standard for office documents. This XML based format means you're not tied in to CALC. You can access your spreadsheets from any OpenDocument compliant software.

Of course, you are free to use your old Microsoft Excel spreadsheets, or save your work in Excel format for sending to people who are still locked into Microsoft products. If all they want to see is your results, then use Portable Document Format (.pdf) - no need to buy any extra software.

More power to your presentations

Save your presentations in OpenDocument format, the new international standard for office documents. This XML based format means you're not tied in to IMPRESS. You can access your presentations from any OpenDocument compliant software.

Of course, you are free to use your old Microsoft PowerPoint presentations, or save your work in PowerPoint format for sending to people who are still locked into Microsoft products. Alternatively, use IMPRESS's built-in ability to create Flash (.swf) versions of your presentations.

The powerful graphics package

DRAW - from a quick sketch to a complex plan, DRAW gives you the tools to communicate with graphics and diagrams.

Import graphics from all common formats (including BMP, GIF, JPEG, PNG, TIFF, and WMF).

Use DRAW's free ability to create Flash (.swf) versions of your work.

The new way to access databases

New to Version 2, BASE enables you to manipulate database data seamlessly within OpenOffice.org. Create and modify tables, forms, queries, and reports, either using your own database or BASE’s own built-in HSQL database engine. BASE offers a choice of using Wizards, Design Views, or SQL Views for beginners, intermediate, and advanced users.

For more information, please see the Base project page at the OpenOffice.org website.