What you can make.
If it is possible to draw, it is possible to print!
Architecture, Toys, Art, Entertainment, Medical, Consumer Goods, Games and anything else you can think of.
The options in what you can make with 3D printers are endless.
It is possible to print objects that are almost impossible to manufacture in a factory, because we do not have the problems with drafts and moldparts of machines.
There is for every material a minimal wall thickness and maximum tolerances that you have to keep in mind. You can find this information on the 3D techniques pages.