Mac: TaskBadges is a simple app that monitors any text-based to-do lists you choose and figures out how many uncompleted tasks you have left. It then puts a badge on the text file so you can always see how many things you have left to finish.
Additionally, all your monitored text files are available in the menubar so you can quickly open them or just see what you've got left to finish. If you manage your tasks in a text file, TaskBadges is an excellent (and free) add-on.
TaskBadges supports three styles of to-do lists: square brackets, todo.txt and TaskPaper. If you already use one of these styles you don't have to do anything -- TaskBadges will automatically recognise completed and uncompleted tasks and assign a badge number accordingly. If you don't use one of these styles, you'll need to adapt or TaskBadges will just assume you have no tasks in the file at all.
While these are all reasonable styles, I really wish TaskBadges handled simple lists, in which each item has a - for incomplete or an x for complete and didn't require square brackets. That's a little nitpick-y, but that's the simplest list format there is, and it would be nice to be able to use it too. That said, TaskBadges is still pretty versatile, useful and free. Go check it out on the Mac App Store.
TaskBadges (Free) [Mac App Store]