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.
GoodGantt - The best Gantt chart for Trello®
Agile Tools for Trello - The one power-up all agile teams using Trello need
Gantt - Create beautiful Gantt charts
Trello for Slack - Organize anything with anyone, inside Slack
Gantt Charts for Zenkit - Track & manage complex projects with a Gantt chart in Zenkit