I've had NotePlan for my Mac and iPhone since the betas. I use it in conjunction with Things 3. The beauty of NotePlan for me is that it allows me to break down tasks for projects quite easily, and then work through them on a calendar-ToDo list. I could do this with Things or OmniFocus, but I like how NotePlan allows me to delineate my tasks within a project without over crowding a GTD program like Things. I may not need both, but I am more productive using them together. One more thing: the developer is great. He seems to be genuinely interested in user input, and her responds to queries and suggestions quickly and thoroughly.