Depending on the context, ZFT can be one of many things in the Fringe universe. There is a group of terrorist/smugglers that specialize in dealing with fringe science that call themselves ZFT. This group acts as the main antagonist for the first season or so, but that's not where it ends. ZFT is also the title of the manifesto that the group is based on. This manuscript tells of a coming war between two parallel universes. While it is incomplete and parts are missing, it speaks of recruits and preparing our children to fight in a war with an alternate universe that far more technologically advanced than our own.
But wait, there's more! In the alternate version of the Fringe universe, ZFT is a book written by their Walter Bishop that outlines terrible natural disasters due to a degradation of their universe. He then reveals that his original hypothesis of it being a natural event is wrong, which leads to his hostile actions towards the universe we know and love. Confused yet? Don't worry, we're all still a little fuzzy on the whole thing.
