Android: Today, Microsoft announced that it is expanding its Office for Android beta. Now, you can install it on any 7-10" ARM-based tablet running KitKat or higher. You don't even need an invite anymore.
Previously, the beta required you to sign up to be eligible, but now Word, Excel and PowerPoint are available for anyone to install. The company is soliciting feedback during the beta, so even if the apps aren't what you need, it's worth trying them out to let Microsoft know what you might want in the future.
Microsoft Excel Preview [Google Play Store]
Microsoft Powerpoint Preview [Google Play Store]