1. Apache OpenOffice

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Apache OpenOffice is a powerful open source suite which includes a word processor, spreadsheet, presentation tool, vector graphics editor, database manager and mathematical equation editor.

The package is generally easy to use. An OpenOffice.org tool acts as a central launcher, and includes wizards to help you create a new letter, presentation and so on.

The applications themselves look and feel much like the pre-ribbon Microsoft Office (they will open most Office documents, too, although the original formatting isn't always preserved).
One problem is that disagreements over the direction of OpenOffice have resulted in many developers leaving the project, and starting the rival LibreOffice. It's not clear how OpenOffice will progress in future, then, but right now it's still a capable suite.

2. LibreOffice

A recent spinoff from OpenOffice, LibreOffice still looks much the same. There's a similar launch screen, and the same core features (word processor, spreadsheet, presentation tool and so on), which look and feel like their OpenOffice equivalents.

There are lots of smaller tweaks, though: improved file format compatibility (including support for all Visio files from 1.0 through to 2013); support for Firefox themes to customise the interface; better template management; colour scales in spreadsheets, a status bar word count in Writer, and so on.

Nothing revolutionary, but LibreOffice is at least making progress, and at the moment it's outperforming OpenOffice.

3. SSuite Office

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If power is your top priority, then SSuite Office probably isn't the program for you. It's more like Office 2003 than 2013, the core applications are relatively limited, and they can't handle OpenXML files (Microsoft's DOCX, XLSX and so on).

For a less demanding audience, though, it could be a different story. The program is easy to use, its word processor and spreadsheet are quite capable of doing useful work, and it also comes with an array of bonus extras: an email client, graphics editor, web browser, security software, media player, formula editor, image viewer, various network tools, even a few games (they're mostly very limited, but still fun to explore). If you're just looking for something relatively simple then SSuite Office could prove interesting.

4. Kingsoft Office 2012

Kingsoft Office 2012 is a fraction of the size of other suites, yet still has the three core tools most people need: a word processor, spreadsheet and presentation creator.
Each of these has a browser-like tabbed interface, making it easy to open multiple documents.

There are lots of attractive templates, Paragraph handling is convenient, an encryption feature helps to keep sensitive documents safe from snoopers, and perhaps most importantly, the program is better at importing Office documents than most of the competition.
It's also only free for personal use, though, and there's no doubt that LibreOffice has more features (vector editing, database management and so on). But if you're a home user just looking for the basics then Kingsoft Office 2012 could be ideal.

5. SoftMaker FreeOffice

SoftMaker FreeOffice is another essentials-only suite, offering a word processor ('TextMaker'), spreadsheet ('PlanMaker') and presentation builder ('Presentations'). These are well-designed and easy to use, though, with a comfortable and familiar interface.

Microsoft Office documents are generally imported very well, each application can export documents to PDF, and although you don't get a dedicated graphics tool, TextMaker has plenty of drawing and image tweaking features.
Overall, SoftMaker FreeOffice is a quality tool, and worth a look if you don't need all the LibreOffice extras.