Visio is a Microsoft Office Suite product (with a different
download and license) that developers and architects use to draw visual
diagrams, drawings and architecture. Earlier this year, Microsoft launched the
latest version of Visio, Visio 2013. Check out new
features of Visio 2013.
Microsoft just announced a free Visio Viewer that will let
you open and view Visio drawings for free. Prior to this, to open and view a
Visio file, you must buy and install Visio on your machine.

From a blog
published by Stephanie Horn on November 28:
The Microsoft Visio Viewer is a free download that lets
anyone view Visio drawings without having Visio installed on their computer. If
you have Visio, you can still benefit from the viewer because it allows you to
preview drawings in both Outlook and the Windows Preview pane. We recommend
that everyone with Windows 7 or Windows 8 download the latest viewer to get the
best experience viewing drawings.
Now you can view Visio files in a Visio Viewer, File
Explorer and Outlook. Visual Studio 2012 can also open a Visio file.