The revamped version of Office Web Apps has been available in preview since July. Over the weekend, Microsoft rolled out the update for all users.
As with earlier versions of Office Web Apps, you don't get an exact replica of every feature found in the desktop Office apps. However, unless you're a power user, there's more than enough here for your needs (and it's a lot cheaper than buying Office). The interface includes the mildly-modified Office 2013 look, chiefly distinguished by using capital letters for Ribbon tab names.
[via Office Web Apps blog]