We've been using https://subtask.co -- it has 3 pretty awesome features which I'm baffled why Trello doesn't have:

- You can break down tasks into subtasks and those subtasks into subtasks themselves, etc

- You can dynamically group task columns by who's working on them, what is their status, what is their goal, etc

- You can arrange what's to be done on an effort-value grid, which helps immensely when choosing what to take on next