Office 2013 has been available to IT pros, enterprises, and developers (read our review) since late last year, and the desktop software hasn't changed in the meantime. (Microsoft has, however, posted system requirements.) But the Office 365 subscription services introduce new features such as Office on Demand for Web-connected PCs. We've heard no word from Microsoft on when Office on Demand for Android or iOS users might be available.
Office on Demand has some system requirements: Windows 7 or 8 and a supported browser, namely Internet Explorer 9 or later, Mozilla Firefox 12 or later, Apple Safari 5 or later, or Google Chrome 18 or later. If you can't run Office on Demand, you probably can still edit documents in Microsoft's Web apps, which aren't as full-featured but can certainly handle basic chores.
Hands-on with Office on Demand
I tried Office on Demand by uninstalling Office completely on my laptop and setting up my Office 365 Home Premium subscription on Office.com. This process involves typing in a product key, much the way you would during the desktop-software installation, and linking it to a Microsoft account; I used my Windows Live account.
I then logged in via Office.com and immediately saw a My Office landing page that showed all my SkyDrive files as well as icons for accessing the on-demand apps: Word, Excel, PowerPoint, Access, and Publisher.
Clicking one of the application links first brings up a tooltip suggesting that you'll be creating a new document, and then produces splash screens informing you that the application is being streamed to your browser (Google Chrome showed a pop-up with more detail about the add-on). The application took about a minute or so to launch--but when it did, it looked like the real deal.
Alternatively, you can click an existing document in SkyDrive and then click an Edit Document link, which gives you the choice of working in the Web app or accessing the full on-demand app. Regardless of how I opened a document, I noted a slight delay in saving to SkyDrive. At one point the app was unable to save to SkyDrive (it said it was disconnected from the server) and saved the document to my hard drive.