Microsoft started a closed beta for Office on Android tablets back in November, but today it's opening things up. Just mosey over to the Play Store, and you can download Word, Excel, and PowerPoint for free, no beta invite required. These are still preview apps, but they seem ready for prime time.
You can install these apps on any Android tablet with a screen between 7 and 10.1-inches that is running Android 4.4 or 5.0. There's a popup warning when you first start an Office app on Lollipop that there may be compatibility issues, but I haven't encountered any problems. You will need a Microsoft account, but the apps are completely free.
The Office apps for Android can be used to edit and create files locally or in OneDrive. If you've got a Dropbox account, Office can plug into that as well. Take 'em for a spin and see what you think. I'm reasonably impressed.