This is a pretty common question: What tool should I use for tracking my Agile project or Sprint?
In my humble opinion, based on what I've been using recently:
If you want a simple display for a few tasks with easy setup and easy start, go with Trello. This is really a visual card column system, Kanban style. It is beautifully ad-hoc, and you get a good usable tool quickly. Create a board, add some columns, add some cards. As easy as that. I find the limits come when you can't fit all the cards on the screen. It also does collaboration surprisingly well. A favourite quick planning tool.
If you're looking for something that definitely pushes you into thinking in Scrum-like Sprints, I'd go with Pivotal Tracker. It has opinions about how you'll plan and work. It organises sprints for you, helps you build and manage a backlog easily. I like this and use it for a lot of my personal and small projects. Pivotal manages sprints and velocity fairly seamlessly and otherwise stays out of the way.
If you've got time for configuration and are on the bigger project side of things, I'd take a look at Atlassian Jira Agile. You get something that is more like a issue tracking system with reasonable add-ons for agile processes. It works well when configured. You will spend configuration time.
And if none of these sound like you: start with an on-line collaborative spreadsheet (e.g. Google Sheets) and use that. If the point is to plan and communicate, you can go a long way with a single spreadsheet with a few tabs.
There are a lot of tools in this space. Ask Google if you want to go deeper.
Or give me a shout and I can chuck in some more ideas.