Have a look at Life Balance. This application, written by some MIT grads, is in my opinion one of the most useful applications for OS X. You define your todos in an outline. Each todo is assigned a priority (on a sliding scale), a timescale (due date, no due date, repeating, etc.) and a "place". The definition of places is where the application shines. Places can contain other places (e.g "Work" can contain "Work-Office" and "Work-Home"). Places can also have "opening hours". Life Balance's "Todo List" then displays a list of the things, in priority, that you should be doing given the time of day, and where you are. For me, as 5:00 p.m. shifts to 6:00 p.m., my todo list begins to change from work stuff to home stuff. It's really an amazing application. http://www.llamagraphics.com/