WeDo is a simple to-do list app. It offers habit tracking in addition to basic lists and tasks.
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Has versions for Android, Web, and iOS.
Pro Supports file attachments
You can attach files to each task.
Pro Great user support
It is a new app, but they have a very good interface so the users can send their suggestions to improve the app.
Pro Users can add recurrent tasks
It allows users to set recurrent tasks.
Pro Supports subtasks
You can add subtasks to any task.
Pro Allows users to assign tasks to other users
It allows you to assign tasks to other person. If he/she does not use WeDo, it sends an invitation.
Pro Clean interface
At least for a while.
Pro Supports groups
You can add groups, and for each group, yuou can add members. It is something like Trello Boards, but I think its better.
Con No calendar integration
Does not have calendar integration