PC Tonic

StarOffice* ~ Sun Microsystems
*****
Available for: Windows 98/ME/2000/XP/Vista, Linux, Unix
Download: Google Pack
Overview: StarOffice is an excellent office suite by Sun Microsystems, brought to you for free through the Google Pack (it would cost you US $70 otherwise). StarOffice comes with a word processor (Writer), a presentation software (Impress), a database (Base), a spreadsheet (Calc), a drawing application (Draw) and an advanced maths tool (Math), all of which are rich in features. StarOffice provides a simple and effective interface and has some nice features like direct PDF export (without need of an external application). It supports the formats of all other major office suites, like Microsoft Office and Corel WordPerfect.
StarOffice home page

OpenOffice.org ~ Sun Microsystems
*****
Available for: Windows 98/ME/2000/XP/Vista, Linux, Unix, Mac OSX
Download: home page | Download.com | FileHippo
Overview: OpenOffice.org is the open source office suite by Sun Microsystems. It has the same set of applications that are present in StarOffice with almost all the features available. Being open source, OpenOffice is highly modifiable and can be customised fully for personal use. OpenOffice.org is community maintained which results is frequent updates are version upgrades. It’s secure code serves as the base for StarOffice.

Symphony** ~ IBM Lotus
***
Available for: Windows XP/Vista
Download: home page
Overview: Lotus Symphony is an Open Document Format based office suite, like OpenOffice.org. One of the latest office suites to join the war against Microsoft Office, Lotus Symphony offers a word processor, a spreadsheet and a presentation software, all for free. The interface resembles that of Microsoft Office 2003 and Office 2007. All the three applications come with a sufficiently large number of features for professional and personal use. Lotus Symphony does have some demerits though – it is still in beta stage, and it is missing some vital portions of an office suite like a database.

OxygenOffice Professional ~ Kami
****
Available for: Windows Vista/2003 Server/XP/2000/ME/98, Linux
Download: home page | Download.com
Overview: OxygenOffice Professional is an enhancement of OpenOffice.org. It addresses the major weakness of OpenOffice.org – lack of sufficient templates and galleries – by including a strong 3400 images in it’s own gallery. There are some other minor modifications too. While OxygenOffice Professional does offer more than OpenOffice.org, it lacks the huge community base of OpenOffice.org.

[Notes]
* StarOffice is available for free only with Google Pack.
** Lotus Symphony is still in BETA stage.