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.
Slack Jira Integration - Easily keep issues moving right from Slack
GoodGantt - The best Gantt chart for Trello®
Sortd for Slack - Get Trello-style project boards right in your Slack!
Paws for Trello - The best way to use Trello on your desktop
Actions from Slack - Turn Slack messages into tickets, issues, tasks, and more.