Without a doubt the best to-do manager we have ever seen

In my experience, Trello is awesome if you are part of a team with more than one customer or project and you also develop internal tools (like shift schedulers, vacation control, etc) where you can't use the customer's ticket tool to document your internal progress. You simply create a board/project with your internal product and manage it from there. Let's use the first example: a shift scheduler. With Trello you can create a board/project with this name and create all internal tasks, like "Application needs to be updated to the last version of nodes", "Resolve bug xyz reported by coworker", "Implement feature abc suggested by our manager" and work from there with subtasks and to-do lists.