Managing projects with online tools is a very powerful approach. It gives you access anywhere to your project information, enable team collaboration, and remove you for the duty to maintain an IT infrastructure.
Many of these tools are based on the waterfall approach, with tasks and sometimes a Gantt Chart.
For those using Agile in your project management methodology, it is a bit harder to find a solution. Here is one that I discovered today. It is called Scrumwise.
From their “About Us” Page
Visit their website:

Michel Dion, PMP, CPA
Founder and Developer of Project-Aria
Discover my book:
Leadership Toolbox for Project Managers: Achieve Better Results in a Dynamic World