The better free todo app

Hello everyone ! I'm currently looking for the best free to-do app in the world! To achieve this impossible quest, I want to found an app that corresponds to this standards : - must be FREE (at least for the next features) - can be interconnected with Google Calendar (as Wunderlist or Google Tasks does it) - the tasks can be : -- time estimated and due to a date and a time (like Remember the Milk) -- repeated -- subdivided into subtasks (like Trello allows it with "convert to card" todo feature, but I prefer Todoist way for this) -- categorized to a custom classification (like "work", "school", ... like Remember the Milk does) -- handle a description text -- assigned to a task list/project -- handle comments (Trello, Wunderlist) - the task lists/projects can be subdivided and be encapsulated as many times as we want (I really love the Todoist method) - task lists/projects, categories and tags can be shared and allow team working (like Wunderlist and Remember the milk) -- we can assign lists/projects member to a task (Trello, Remember the Milk, Wunderlist) Secondary features that can be very cool : - API - Interconnection with Slack and Trello Services I already tried : - Trello (a little bit complicated for using it as a todo even if it matches almost all my needs) - Google Tasks (too simple, cannot be shared, no subproject, too simple subtasks) - Todoist (perfect but paying) - Wunderlist (Almost perfect, it just lacks some tags system and infinite subdividing lists and projects) - Remember the Milk (pretty perfect except the subdividing feature that I love so much is only on paying plans) As you can see, I love todos. If you find me the perfect app, you're going make me more than my day! So that the game begins as we say.