Which Thing First (WTF ) is a super-simple way of working out your priorities, letting you discover the most effective order of doing things. Getting Things Done (GTD) by Dave Allen is a great productivity tool. But how do you know which Thing to Get Done first. 'Which Thing First ' helps you work it out by asking a series of questions, forcing you to consider each task against each other. This FREE version of the app is fully functional, but limited to 4 tasks.