WordToys
Make Word easier to use and more fun to work with.

MiKTeX
Write mathematical expressions within text documents easily.

Rainbow Analyst Personal
Develop your own Excel financial models and check models developed by others.

2007 Office Sample: IMsoDocExporter Header File
Offer alternate add-ins for PDF, XPS, or other fixed-format.

Sagata DOE Toolset
Get a DOE package for your MS Excel.