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.

Userfeed - Product feedback made for Intercom

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

Fider - Fider is an open source, cross platform and free to use customer feedback platform for companies...

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.

ClearFlask - Open-source Product Feedback Tool with a Public Roadmap and Announcements.