Calc is OpenOffice's spreadsheet application and, as with Writer, compares very well to its Microsoft Office equivalent. Treated as a standalone product, Calc is efficient and comprehensive in terms of its features.
Anyone who has used Excel will be familiar with the Calc interface: although it isn't as slick as the latest Office release, it's certainly as usable as previous versions. Calc is reported to struggle with particularly complex Excel files and formulae, although we encountered no problems - and it does support a wide range of file formats.
Calc uses a range of functions to create formulae for data calculations. The Function Wizard simplifies this task, but you need a good mathematical understanding. While documentation is extensive, it can be quite technical and difficult to navigate.
As in Excel, spreadsheets can have multiple worksheets for building up complex arrays of data, what-if calculations and creating dynamic charts. And most of Excel's advanced features, such as Pivot Tables - DataPilot in Calc; used to analyse large amounts of data - or the ability to link to an external HTML data source, are available.
There are a few areas where Calc is outdone by Excel. If you appreciate Excel's charting options for creating all kinds of scatter diagrams, pie charts and bar graphs, you could be disappointed with Calc's slightly curtailed range of options. However, the vast majority of Excel users are simply confused by its excess and can afford to stick to the more limited, albeit logical, selection in Calc.
Writer and Calc are the most important components of the OpenOffice suite, but we should mention how the other applications compare to their Microsoft equivalents. Impress is far inferior to PowerPoint in terms of templates and guidance, but is much improved in version 2.0. Base is a complex but sophisticated relational database.
The other two applications, Draw and Math, do not have an exactly matched equivalent in standard versions of Microsoft Office. Despite its name, Draw is better thought of as a charting tool equivalent to Visio than as a competitor to CorelDraw or Illustrator. Math enables users to create complex equations, which is traditionally very difficult using word processors, but Microsoft does provide an add-on for Word.
For a free application, Calc comes highly recommended. OpenOffice 2.1 is incredibly useful and feature-rich, especially when you consider that it requires no financial outlay. Compatibility with Microsoft applications is good and performance has been greatly improved. However, it's not as feature-rich as Microsoft's Office suite, particularly if you require collaborative tools.