Getting Things Done (aka GTD) is both, and the workflow ideas introduced in that book. It has a strong almost cult-like following. I read the book a few years ago and was converted. It was really a life-changing book.
Here’s the super simple explanation of GTD: Your life is filled with “open loops,” which are things you have to do, delegate, defer, or drop. GTD is a system for collecting those open loops, breaking bigger loops (“projects”) into discrete actionable tasks, assigning a context to each task based on what resource you need or situation you must be in to accomplish it (i.e. Phone, internet, grocery store, home, office), and figuring out a “next action” for each project (which is the next task you could do to move that project forward). That’s it, in a nutshell. You gather and process like that, and when you’re ready to get some things done, you work based on context. So if you’re on the train, and you have access to your phone and an Internet connection, you can do any of your next actions that have an “Internet” or “phone” context.
Things that have a “home” context don’t concern you, because you’re not at home. Things that are “phone” context but aren’t next actions don’t concern you because you have to do something else before you get to that. The idea is that you get these open loops out of your head, where they rob you of your focus, and into a system you trust. Once they’re in a system you trust, these things magically stop bothering you.
They’re in a system, and the system worries about keeping track of them, not you. Seriously, go buy the book — it’ll blow your mind how much sense it makes. In the last couple years, “GTD apps” — software applications that keep track of your open loops, and show you your next actions for a given project or context — have exploded onto the scene. The most notable is probably, an OS X application (with an iPhone component)., a well-known GTD advocate and a productivity visionary in his own right, was hired to consult during the development of OmniFocus. I use OmniFocus. It’s certainly capable — but its UI is too complicated, and it is held back by the same quirky UI used by its creator for their other applications (where that UI makes a little more sense). It almost feels like they copy/pasted large portions of their other software together to make OmniFocus.
GTD Times reader Heather asked: I’ve been feeling really in the zone with GTD lately. I know what I need to do, the system is working, BUT the “waiting fors” are going to give me a stroke. I use the Things for Mac application and noticed that consistently about 25-30 percent of my next actions. Getting Things Done & OmniFocus 2. Here’s the specific stuff. OmniFocus is the best way to implement GTD on Mac and iOS. Capturing in OmniFocus. The Inbox The Inbox is where capture happens.

At times, using OmniFocus feels like its own set of open loops! There are all these buttons and menus and views and stuff that you’re not using, but you have to think about every time you open the app.