OpenOffice is a free open source multi-platform, multi-lingual office suite project and is compatible with all other major office suites such as Microsoft Word and Excel. As of version 3 OpenOffice now also runs natively on Mac OS without any addons.

OpenOffice includes several components you would expect to find in an Office Suite.

• Writer word processor
• Calc spreadsheet
• Impress presentation software
  
• Draw vector drawing program
  
• Math for creating mathematical diagrams

Each of these components works seamlessly with each other so a written document can be embedded in a spreadsheet or the other way round. The Impress presentation package has many useful features and slide transitions including making custom transitions.

OpenOffice also supports Microsoft's VBA although not everything is guaranteed to work. Although OpenOffice does have it's own scripting language.

All in all this a very good all round alternative office suite and doesn't cost a penny for home or commercial use.