FRAMEplus 5.0 available at www.frameplus.net
This is a window energy analysis tool used by professionals in the window design and testing fields.

RETScreen available at http://retscreen.gc.ca
This is a building energy analysis tool with a passive solar module that can be used to compare the financial effect of various window options.

CATALOGUE available at www.enermodal.com
This is a listing of windows and their ratings. Some are certified and some are not.

Enerpass available at www.enermodal.com
This is a building energy analysis tool.

Advanced Buildings at www.advancedbuildings.org
Shows some of the new technologies under Structures.

Energy Efficient Windows Collaborative at www.efficientwindows.org
Energy efficiency information from the US perspective.