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.

Taiga - Project management platform for agile developers & designers

Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.

Craft.io - All-in-one product management software for entire product lifecycle

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

TargetProcess - Agile Project Management Web Application