The rules for AF4-3T can be found by clicking here.
As its name suggests, this system is a combination of AF4 and the 3T Method, in which AF4 is used to feed 3T with tasks.
It is more thorough than AF4 because of the emphasis on finishing tasks which 3T brings. Because unfinished tasks do not get re-entered in the Open List, the Open List is more manageable than in AF4
It has the same disadvantage as 3T in that progress can be slow if more than one large task is included in the three tasks.
This is a very powerful method and represents a considerable step forward in the efficacy of these systems.