Aluminum System Windows and Doors That Are Pre-Engineered - Right Work (TOSTEM) Find What You're Looking For Exactly. We have been happy to provide TOSTEM pre-engineered windows for homes, hotels, and commercial buildings. The largest producer of pre-engineered windows and doors in the world is TOSTEMS, a Japanese company. provides you with the best pre-engineered windows that have a 40-year warranty and can withstand severe rain. Using a comprehensive range of options that guarantee your windows and doors will have comfortable and feather-touch use features. You can rethink your living space with the help of our tailored solution.