Microsoft does not make a Project viewer like they have with Visio or Word.
I believe that there this at least one company who produces a commerical
viewer, but it is not free.
What is your need for a viewer? Couldn't this need be addressed through
appropriate Views in Project Web Access, or by exporting the project to a
Web page?
Please see FAQ Item: 16. Project Viewer. FAQs, companion products and other
useful Project information can be seen at this web address: http://www.mvps.org/project/
Hope this helps - please let us know how you get on