Today at the SharePoint Evolutions 2013 Conference I announced my latest pet project called Open WOPI. Open WOPI is an open WOPI client that allows you to extend SharePoint 2013, Exchange 2013 and Lync 2013 with file previews and editors for any type of file formats.
The project is now (at least very, very soon) available to download from openwopi.codeplex.com and is published under the Ms-PL license. This is currently an early beta (or what you would like to call it) but will be improved over time.