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.

yuuflow - Simple yet flexible project management

Nifty - Manage projects, work, and communications in one place.

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.

Height - Height is a project management tool for your whole team.- Task lists to keep your team synced- Chats to keep conversations about work in one place- Lightning fast with Cmd-K, custom shortcuts, and jump to- Integrations to automatically update tasks

Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.