I have been searching far and wide for a to-do list app that stands up to the challenge of my busy life. Most recently I have taken to trying out Wunderlist, a highly regarded app in the world of to-do lists. They have a beautiful and clean UI and the ability to customize the background of your to-do list (limited choice of backgrounds unless you upgrade to pro for 4.49€). While the app and the web site have an extremely nice UI there are a few very big features that I found to be lacking.Collaboration in free version
Most of the other free to-do apps give you at least the ability to collaborate with a severely limited number of people you can collaborate with like between 2 and 5. Wunderlist does not allow any collaboration between users on a free account. This was a big turn off because sharing to-do lists even with a small group is a big deal and without a free version there is no way to test the group features without paying for the app which I believe both users have to be upgraded for collaboration to work.