Cellular machina - Nano machines for assembly purposes.
Someday in the not too distant future we will use nano-machines to replicate our bodies… oh wait, we do this already. In fact, this trick has been happening for a really long time.
Watch this video! around \~2:30 you get to see DNA “spinning as fast as a jet engine” through an existing nano-machine. What happens when we can give instructions to these machines?
Think about all the cool things that are built with DNA already… imagine if we could make trees grow into buildings, instead of cutting trees apart then reassembling them as buildings.
What do you think would be the most helpful tool for humanity that could be built with this new class of machine?