eyeOS, bought by Telefonica in 2014, is developing an open source alternative to Office365. It is called Open365 - not that creative. Nevertheless, it looks good, it feels good and there are sync clients for Linux, OS X and Windows. Open365 provides LibreOffice Writer, Impress and Calc, a calendar and an address book.
In the next few weeks eyeOS will provide a download and therefore the possibility to have Open365 on premises. And this might be important for some of you! I think you should give it a try, in the cloud or on your own machine.