Mac: If you find that procrastination often gets the best of you and you need help focusing on your work, Focusbar is a free utility that can help you out. It pays attention to what application you're using to do your work and bugs you when you sneak off to do other, less productive things.
For example, if you're trying to focus on email then Focusbar will display a little bar with a reminder about your current activity until you go back to what you're supposed to be doing. When you're doing a particular activity, you can just head up to your menu bar and let Focusbar know you've finished. If you find it's being too annoying or not annoying enough, you can also specify just how much you want it to bug you with a handy slider. It's a very simple app but can be very effective if you need a persistent reminder to help focus on your tasks.
Focusbar (Free) [Mac App Store]