Wunderlist was a ubiquitous listing app that allowed you to list things as varied as your ideas, things that you need done, and places that you want to see.
Whether sharing a grocery list with a family member, working on a personal or group project, or planning a personal vacation, Wunderlist aimed to make it easy to share and collaborate on your lists with everyone in your life.
Wunderlist featured instant syncing between your phone, tablet, and computer to allow access to your lists from anywhere. This made Wunderlist a sort of task management and collaboration app powered by a list-based structure.
At this point, Wunderlist has been succeeded by Microsoft To Do, which is also free and aims to do many of the same things that Wunderlist did. That said, if you aren't a fan of the new layout or generally avoid Microsoft software and services, there are plenty of other free Wunderlist alternatives that are still in active development.