You’ve been granted magical engineering skills, but you can only use them to build on badge or machine. What do you build?
For well over one hundred years a book has been the greatest technological efficient machine available to the masses, and now currently available electronically.
If granted the skills, I would engineer the ability to provide everyone on the planet with a tablet of some type with access to the libraries of the world, and free educational programs from pre-school to post graduate degrees for free.
Now, if someone invents a device encouraging everyone to find a desire to read while limiting mass media to only three hours a day. I think that would be the world’s best gadget for the advancement of humanity. 🙂