You can also use Google Docs offline now. It's free, good, and most importantly it's reliable. At least, that's been my experience with it.
I believe Microsoft have also made Word, Excel, and Powerpoint web editions to compete with Google Docs which are also free on
http://office.live.com. But I don't know if they have offline versions. Oddly enough, all three are totally free on Android and iOS.
They're more or less the same, it just depends on which account/ecosystem you prefer: Google or Microsoft.
My experience with LibreOffice was pretty good too. It's not just a good alternative to MS Office but a well put-together suite overall.
I also tried our Polaris Office (
https://www.polarisoffice.com) a while back, it came pre-installed on a laptop, and it was not bad too. They have free version and a paid version though.