Check out the LibreOffice productivity suite (pictures)

When you think office suite, there's a good chance you're thinking about the word processor. In LibreOffice's case, that's Writer: it does everything you'd expect from a modern Microsoft Office clone, including support for comments and tracking changes between multiple users. It will also read older Office documents that Microsoft Word has abandoned, which could come in handy if you have old Word files kicking around.

Microsoft Excel remains the gold standard in spreadsheets, but even folks with complicated needs will find a lot to like in LibreOffice's Calc. Simple Excel files I've tested are imported flawlessly, and while more complicated sheets weren't always accessible I found I could generally duplicate their functionality using Calc's own tools.

I've never made a PowerPoint presentation, but if I ever had to, LibreOffice's Impress wouldn't be a bad choice. It's compatible with PowerPoint, so you shouldn't have trouble passing files around the office, and lets you embed images, charts, and video or audio files right into your slides.

Draw is a powerful diagram creation tool that doesn't actually mimic anything in the Microsoft Office toolkit. You can use it to quickly create flowcharts and sketches to tuck into existing documents or wherever you'd like.

Math functions like the Equation Editor you'll find in Microsoft's Word. You can use it to quickly create mathematical formulas with proper formatting using the standalone app, or within tools like Writer.