Todoist is a popular to-do list app ranked last year by Forbes as the #1 task manager in the world and by Google as one of the best Android apps of 2014. Todoist has apps on every other popular platform(13 in total) except modern Windows. They already have a Windows desktop app which you can download it here. Todoist has recently announced that they have acquired TaskCrunch to-do list app in Windows Phone Store and the developer behind this app is joining Todoist team. He will be the first developer dedicated solely to Windows platforms and you can expect a official Todoist app in Windows Phone Store in the coming months.
For now, you can check out TaskCrunch app here.