www.autodesk.de has an extended post on how to view Revit files for free at this link:
Autodesk – Autodesk Revit Viewer Free

The page reviews the following methods (none of which are very exciting):

For Revit files There are various possibilities.

Display native Revit files
  • Revit installation in viewing mode
Viewing exported data
  • Viewing DWF in Autodesk Design Review
  • DWF viewing in Internet Explorer
  • DWF Viewing into NavisWorks
  • Viewing in NWD NavisWorks Freedom

The English equivalent to the .de page is considerably shorter:

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Scott D Davis
12 years ago

Native RVT Free Viewer? How about Vasari? It's free, lightweight, runs as an EXE with no install, and can open any Revit RVT file in the same version. Current Vasari is built on Revit 2012.