Sidequest creates helpdesks and task ticket queues entirely inside Slack, combining the best features of helpdesk systems and modern task managers.
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.
Halp - Slack-first ticketing for internal helpdesk
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.
Roby - Refreshingly simple helpdesk for Slack & Teams users
Basecamp - A simple and elegant project management system.
Halp for Microsoft Teams - An internal help desk built into Teams