How close are we to a theory of everything?

Since well before Einstein, it was the dream of those who study the Universe to find a single equation to govern as many phenomena as possible. Rather than have a separate law for each and every physical property the Universe has, we could unify these laws into a single, overarching framework. All the laws of electric charge, magnetism, electric currents, induction and more were unified into a single framework by James Clerk Maxwell in the mid-1800s. Ever since, physicists have dreamed of a Theory of Everything: a single equation governing all the laws of the Universe. What progress have we made? That’s the question of Paul Harding, who wants to know:

Has science made any progress with regards to the Grand Unified Theory and the Theory of Everything? And could you elaborate on what it would mean if we did find a unified equation?