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.
ProdActiveLab - Personal productivity and collaboration tool
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.
Timeline.io - Visual collaboration tools for devs, designers, and clients.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Evrybo - Free design collaboration and prototyping tool