Update: Wunderlist has since been discontinued. You can check out Wunderlist alternatives suggested by CNET.
Wunderlist used to be an attractive to-do list service that was accessible both via the web and through mobile apps. It allowed you to add tasks that you need to get done, an optional due date and optional reminders. Reminders could be sent via email or desktop notifications on Firefox and Chrome. Mobile phone users could also get task reminders via push notifications.
Related: Tech Tip: Create an online things to do list with Todoist