The key to being productive (and managing anxiety) is using tools to keep track of things that you have to do… and, most important, hiding things that you will have to do at some future time but don’t need to do now.
We think that one of the reasons we have this state called “anxiety” is because in human history there has only been easy access to task managers in the last two decades.
Anxiety is a poorly designed system for reminding you of things that you have to do sometime soon.
It is poorly designed because it doesn’t allow you to schedule reminders for a particular time or situation. So, instead of that you waste brain power continually tracking that particular task over and over again until finally it is time to take action. 
With that in mind we suggest that the key function of task managers is their ability to hide the huge list of things we should (or could) do until those things are timely or appropriate.
So, in assessing a task manager consider how flexibly it calls up tasks. An ideal app would do at least the following things –
- Allow you to write down great ideas that don’t have any particular due date (“future projects”). You want to capture those “great ideas” somewhere, but if you are like us less than half of those great ideas will survive a subsequent review. The rest can be deleted. But that winnowing process can’t take place when you are “brainstorming” and coming up with creative new projects. The process of brainstorming and editing a list of ideas involve completely different states of mind.
- Allow you to schedule tasks by date (ideally also by time) and context (I have tasks that I can do on the phone, those I can do on the computer, those that involve talking to a colleague, those that involve shopping or driving someplace specific, etcetera) and, possibly, also by location (things you need to buy at Target, say).
- Allow you to assign tasks to others (if you are part of a team)… And to look up those tasks when you are at your computer, or your phone, or…. In other words to have a web interface, an iPhone interface, and an Android interface; and to allow sharing via the internet.
- Allow you to email ideas to your task manager (so that if you have a great idea but can’t write it down entirely you can at least send it to your list for later editing).
Here are some apps that others have found useful –