Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Asana Boards - A simple, visual way to track your team’s work
TaskBoard - A Kanban-inspired app for keeping track of things that need to get done.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
Pintask - Pintask is the most customizable Kanban board.
Elegantt for Trello - The most elegant way to manage your Trello projects