The Spacex Falcon Heavy will be the most powerful rocket in the world that will be currently flying. There have been more powerful rockets but they are no longer flying. The Falcon heavy will be capable of launching 64 metric tons into Low Earth Orbit. This was relatively recent improvement from improved design and improved engines.
Only the Saturn V moon rocket, last flown in 1973, delivered more payload to orbit than Falcon Heavy. The Russian Energia rocket had the capacity to launch 100 tons into low earth but only had two launches which did not launch large payloads.
The Falcon Heavy has 27 first stage engines.
The Falcon Heavy will be used to launch two civilians on a lunar orbital mission Moon in 2018.
@elonmusk Please Elon, please tell us when the Falcon Heavy will launch.
— Johnny Grinter (@JohnnyZenith) June 8, 2017
All Falcon Heavy cores should be at the Cape in two to three months, so launch should happen a month after that
— Elon Musk (@elonmusk) June 8, 2017