||A constructor, but more! Capable of creating more complex parts out of more and more complex parts! A lot of complexity in such a deceptively small building!
||~ Caterina Parks's Assistant,Steve
The assembler, as shown on the official site.
The assembler is a machine used to craft advanced items automatically, from two ingredients. It is an advanced equivalent to the Constructor.
The Assembler, as described, is likely a more advanced version of the Constructor. It's capable of creating more complex products from more complex input materials, perhaps objects such as advanced circuits or computers. Due to this higher level of complexity, the machine will likely cost more to craft.
As shown in an official game play video, the assembler has two belt inputs and one output. It only accepts resources when a recipe is chosen in the machine menu.