Getting Things Done ("GTD") is an approach to task management by David Allen (Author) in his books Getting Things Done (Book) and Making it All Work (Book).
Although there are probably thousands of tools used to conduct GTD, the process itself is what David Allen's approach prescribes and something most task management tools tend not to be too opinionated about.
My preferred task management application is Gqueues (App), which works well for the various steps in my GTD workflow. (see Using Gqueues for GTD).
💡 More of my tools, services, and media preferences can be found on Uses.