An additional application next to Exchange Server 2013 is a new server product called Office Web Apps 2013. The Office Web Apps server can be used to render Microsoft Word, Excel and Powerpoint file types. Other than this the Office Web Apps server is used by Exchange Server 2013 to provide the Web Ready Document Viewing, something that was made available by Exchange Server 2010 natively (although a non-Microsoft engine was used to achieve this).
Installing Office Web Apps 2013
Office Web Apps 2013 can be installed on Windows Server 2012 or on Windows Server 2008 R2, but I prefer the first (due to support lifecycle). If you plan to use the latter make sure that you install the .NET Framework 4.5 and Powershell 3.0, these are installed by default on Windows Server 2012.