Gadgeteering:Modifying and Inventing Devices=>http://www.sjgames.com/gurps/books/Lensman/outtakes/lensgadg.html
Science and Technology=>http://www.io.com/~bolie/Tech/
Dr. Kromm's Patented Math and Physics Tutorial=>http://www.sjgames.com/general/guidelines/writers/math_tutorial.html