These responses are great, but it doesn't seem to actually answer the question (or at least, the question I'd like an answer to). See, I'm in the market for something similar. By the way, I'm not looking for "free", I'm looking for "functional".

I'm coming back to GTD after 4 years of, well, not getting things done. I originally did it all using just note cards, as simple as it gets; it more or less worked if I paid attention to it (there's the rub!).

I have an iPhone now, but ALL my computers are Windows computers (work, home, otherwise). The iPhone syncs well with iTunes and my gmail account and my work Exchange account. So, I generally have no "cross-platform" issues. For GTD, however, there seems to be a gap. Granted, I have no idea what's available, which is why I'm here. But, what I want is simply this: a Windows client application that is designed for the GTD methodology that has a corresponding iPhone app that affords synchronization between the two.

My justification for this seemingly ludicrous request is this: If there's a lot I need to collect or a lot I need to process, tooling around on my iPhone just isn't fast enough; as intuitive as the touchscreen is, I can't type 100 wpm on it, and for the way I visually process things, screen real estate = speed. And, if it isn't fast enough, I'm generally not going to do it. But, I don't always have my computer in front of me when I think of a new "thing" to collect, or when I have a thing to actually do. But I almost always have my iPhone. So, I'd like a robust Windows app that allows me to collect and process in an environment where I'm most productive, with iPhone synchronization so it's portable when I need it to be.

Anyone have a line on something that does this?

Again, simple requirements: I want to do GTD using a desktop Windows computer, an iPhone, and nothing else.